The one unforgivable sin in Islam is something that the Quran describes as "setting up partners with Allah":
"Verily, Allaah forgives not that partners should be set up with Him (in worship), but He forgives except that (anything else) to whom He wills; and whoever sets up partners with Allaah in worship, he has indeed invented a tremendous sin." [an-Nisaa� 4:48]

This sin is given the name shirk, which I believe comes from an Arabic root meaning "to share".

But what, exactly, is shirk?  I have heard it applied to everything from idolatry to polytheism to atheism to paganism (whatever that is) to greed (worshipping wealth) and a whole lot more.  It seems like shirk is treated as a catch-all for just about any wrong belief.  It also seems to me that that can't be right.  Surely Allah must have had something very specific in mind for so grievous a sin that it could never be forgiven.

I'd like to hear what Muslims think the phrase "setting up partners with Allah" means.  I have my own idea, which you may have already read on another discussion, but I'll try to keep my own (non-Muslim) thoughts out of this at least to begin with.

When we say La ilalaha illal la - There is no God but Allah, then all our worships {Ibadahs} shud be for Him alone. When we do believe in that there is only one God, then why is there any need to ascirbe partners to Him ? When He is our Creator, why shud we associate any other false ones.

Ron Webb wrote:   I'm not sure what any of this has to do with "associating partners".  Just because I love money more than Allah does not mean I think of money as a partner to Allah.  On the contrary, if I choose money over Allah, then money is a competitor, not a partner, isn't it?  It is wrong, of course, but I don't see why it is shirk.

Dictionary Meanings
The root of this word consists of the three letters, alif, lam, and ha and the connotations of various derivations, as one finds in lexicons are as follows:

	Became confused or perplexed.
	Achieved peace and mental calm by seeking refuge with someone or establishing relations with him.
	Became frightened of some impending mishap or disaster, and someone gave him the necessary shelter.
	Turned to another eagerly, due to the intensity of his feelings for him.
	The lost offspring of the she-camel rushed to snuggle up to its mother on finding it. Became hidden, or concealed. Also, got elevated.
	Adored, offered worship to.

1. Foremost among the factors which engender a sentiment of some degree of adoration for some one is a person's own state of being in distress or need. He cannot even conceive of worshiping someone unless he has reason to believe that someone to be in a position to remove his distress, to fulfil his needs, to give him shelter and protect him in time of danger, and soothe his troubled heart.
2. It goes without saying that the above belief is accompanied by a belief also in the superiority of the other in status, power, and strength.
3. It is also a matter of fact that where any of the needs of a human being are met under the ordinary process of give and take, which takes place perceptibly before one's own eyes, it leads to no sense of reverence, much less of adoration, for the other. For example, if I should be in need of money and, having applied for, and been given a job, am paid for it, since the whole transaction would take place within the full ken of my senses, and I would be fully aware of the circumstances or the reason for giving me the money, I would experience not the slightest desire to offer my employer any adoration. That sentiment arises only when there is some element of mystery surrounding the personality, the power, or the ability of the other to fulfil peoples' needs or to influence events. That is why the word chosen to denote an object of worship includes in its meanings the senses of mystery, perplexity, and superiority in status, etc.
4. Lastly, it is only natural that if one believes another to be in a position to fulfill one's needs, to provide shelter and protection, to soothe a disturbed heart and fill it with peace and calm, one turns eagerly to that person as a matter of course.

abuzaid wrote: As per hindu, what made you to think that they Don't believe in Allah? Agreed that they worship many dieties but they do believe in a Lord who is creator of Heaven and earth. He is called Eshwar or parmatama in hinduism.

I think you mean Brahma, and beyond being the Creator he bears little or no resemblance to Allah.  Frankly, I think it's absurd to equate the two.  Brahma is only the creative aspect of the Hindu trinity, along with Vishnu (the Preserver) and Shiva (the Destroyer).  You might be closer to compare Allah with Brahman, which encompasses all three aspects and represents the whole Universe; or Atman, the spirit form of Brahman which exists within all of us.

Now, my point is that it is not possible for a person to believe that somebody else other than Allah is god(ilah) in all respect.

If that is your point, then I don't think we can discuss it further.  I'm sure you would be offended if a Hindu were to tell you that it is not possible for you to believe what you believe.

There is no fixed belief in hinduism, almost everyone among hindus have his own idea of religion and God. For a person to be hindu it is not necessary to believe in trimurthy (Brahma, Vishnu and mahesh or shiva). Whoever claim to be hindus and does not associate himself with any other religion is hindu.

abuzaid wrote: This is testification indicates inherent belief in Allah, irrespective of claim of that person. Even when an atheist claim that he does not believe in God, he does.

Are you saying that all atheists are liars?  Or that they believe in God, but they just don't believe that they believe?

The verse that talks about shirk being unforgivable is in case of not repenting. God may forgive others sins if a person dies without repenting also.

The verse doesn't say anything about repenting, and I would have thought that repentance is a prerequisite to forgiveness anyway.  Is there some other verse in the Quran that suggests to you that shirk can be forgiven if the sinner repents?

Very true brother. It is proven right here.

Ronn Webb said :
The verse doesn't say anything about repenting, and I would have thought that repentance is a prerequisite to forgiveness anyway.  Is there some other verse in the Quran that suggests to you that shirk can be forgiven if the sinner repents?

Read these verses

53. Say: "O My servants who have transgressed against themselves! Despair not of the mercy of Allah, verily, Allah forgives all sins. Truly, He is Oft-Forgiving, Most Merciful.
54. "And turn in repentance (and in obedience with true faith) to your Lord and submit to Him before the torment comes upon you, (and) then you will not be helped.
55. "And follow the best of that which is sent down to you from your Lord, before the torment comes on you suddenly while you perceive not!
.
This Ayah is a call to all sinners, be they disbelievers or others, to repent and turn to Allah. This Ayah tells us that Allah, may He be blessed and exalted, will forgive all the sins of those who repent to Him and turn back to Him, no matter what or how many his sins are, even if they are like the foam of the sea. This cannot be interpreted as meaning that sins will be forgiven without repentance, because Shirk can only be forgiven for the one who repents from it.

Say: "O My servants who have transgressed against themselves! Despair not of the mercy of Allah

Except those who repent and believe, and do righteous deeds  (25:70)

Prophet {Pbuh} said, ""O My servants who have transgressed against themselves! Despair not of the mercy of Allah, verily, Allah forgives all sins He does not reckon him Truly, He is Oft-Forgiving, Most Merciful.'' .This  indicates that what is meant is that Allah forgives all sins provided that a person repents. Additionally, one must not despair of the mercy of Allah even if his sins are many and great, for the door of repentance and mercy is expansive.

abuzaid wrote: Don't you think it is better for you to ask about Islam rather than teaching us our own religion??

That is quite an ironic remark from someone who has spent much of the previous discussion trying to convince me that he knows what Hindus, atheists and others believe better than they do themselves.

Let's look at the passage you quoted (25:68-70) in even larger context:

25:63  And the servants of (Allah) Most Gracious are those who walk on the earth in humility, and when the ignorant address them, they say, "Peace!"; 25:64  Those who spend the night in adoration of their Lord prostrate and standing; 25:65  Those who say, "Our Lord! avert from us the Wrath of Hell, for its Wrath is indeed an affliction grievous,- 25:66  "Evil indeed is it as an abode, and as a place to rest in"; 25:67  Those who, when they spend, are not extravagant and not niggardly, but hold a just (balance) between those (extremes); 25:68  Those who invoke not, with Allah, any other god, nor slay such life as Allah has made sacred except for just cause, nor commit fornication; - and any that does this (not only) meets punishment. 25:69  (But) the Penalty on the Day of Judgment will be doubled to him, and he will dwell therein in ignominy,- 25:70  Unless he repents, believes, and works righteous deeds, for Allah will change the evil of such persons into good, and Allah is Oft-Forgiving, Most Merciful, 25:71  And whoever repents and does good has truly turned to Allah with an (acceptable) conversion;- 25:72  Those who witness no falsehood, and, if they pass by futility, they pass by it with honourable (avoidance); 25:73  Those who, when they are admonished with the Signs of their Lord, droop not down at them as if they were deaf or blind; 25:74  And those who pray, "Our Lord! Grant unto us wives and offspring who will be the comfort of our eyes, and give us (the grace) to lead the righteous." 25:75  Those are the ones who will be rewarded with the highest place in heaven, because of their patient constancy: therein shall they be met with salutations and peace, 25:76  Dwelling therein;- how beautiful an abode and place of rest!

The passage gives a long list of virtues to strive for and sins to avoid.  Inserted in the midst of that list is a parenthetical warning (which I have coloured blue for clarity) that for one sin in particular ("any that does this", 25:68), the penalty is doubled, unless the sinner repents.  That one sin is the last one mentioned: fornication.  If 25:70-71 was intended to refer to the last several sins (i.e., to include shirk, which is three sins back in the list), 25:68 would have to say "any that does these".

Ronn webb said :

Yes it does, but you'll notice that it refers only to those "who have transgressed against themselves" (and I suppose fornication would be an ideal example of that).  Shirk is surely on a higher level, a transgression against Allah Himself.

It does n't matter, what you or me suppose. For we believers, it matters that what  Quran and sunnah teaches us.

Al-Bukhari recorded that Ibn `Abbas, may Allah be pleased with him, said that some of the people of Shirk killed many people and committed Zina (illegal sexual acts) to a great extent; they came to Muhammad and said, "What you are saying and calling us to is good; if only you could tell us that there is an expiation for what we have done.'' ------.

NOTE THOSE IN BOLD AND COLORED FOR YOU. Those people commited all the major sins. Apart from fornification, shirk and murder are also major sins.One who commits sins trangress against his ownself. He drags himself towards hell. 

Its not that i think. Its the Quran and hadith that explain us and we obey it. They are n't contradicting. Just read below explanation.

4 :48. Verily, Allah forgives not that partners should be set up with Him (in worship), but He forgives except that to whom He wills; and whoever sets up partners with Allah in worship, he has indeed invented a tremendous sin

As said we need to go thru its commentary. I don't think that you shall be accepting it since you are n't willing so. TO benefit other readers ,{especially as its  posted at non-muslim section} , so that they  shall not get into any misconception, here it is. Am merely repeating the gyst of brother AbuZaid's post..

Here is the commentary of Ibn Kathir for the verse 4 :48

Verily, Allah  forgives not that partners should be set up with Him (in worship),) meaning, He does not forgive a servant if he meets Him while he is associating partners with Him, (but He forgives except that) of sins, (to whom He wills) of His servants.

Imam Ahmad recorded that Abu Dharr said that the Messenger of Allah said, Allah said, "O My servant! As long as you worship and beg Me, I will forgive you, no matter your shortcomings. O My servant! If you meet Me with the earth's fill of sin, yet you do not associate any partners with Me, I will meet you with its fill of forgiveness.''

This hadith explains us that while in the state that we meet Allah swt,  if we do repent and not associate any partners , we shall be forgiven.

I don't understand, when Allah swt is the Forgiver and is ready to forgive any of our sins when repented, then what's your problem. Why are you creating fuss about it. Its so simple here that even major sins like shirk are also forgiven. And why does it matter when Allah swt specifically says or general. Few minds need specific reminders and few understand them in general.  Its the style of Quran!!!

You need not go anywhere Ronn 

Read the same verse.

Verily, Allah forgives not that partners should be set up with Him (in worship), but He forgives except that to whom He wills; and whoever sets up partners with Allah in worship, he has indeed invented a tremendous sin.

Now, carefully read again  - partners shud be  SET  up with Him. And the other part  - whoever SETS UP partners with Allah swt.

But yes, final word, while meeting Allah swt, if he is in the state that he did not repent and associated partners with Allah i.e , in the state of shirk then he shall be punished. Hope, atleast NOW, you understand it. May Allah swt, give all of us its understanding.