Respect your elders , Obey your parents , Avoid polytheism / shirk / joining partners in worship with Allah , Avoid lying / deceiving people through false oaths .

The Prophet Muhammad ﷺ warned against the biggest sins, which are known as Al-Ka'ba'ir. These sins include joining others in worship with Allah, taking a false oath and being undutiful to one's parents. Joining others in worship with Allah is considered a major sin because it is an act of polytheism or shirk that goes against the teachings of Islam. Taking a false oath is also considered a major sin because it involves lying and deceiving people for personal gain or benefit. Lastly, being undutiful to one's parents is also considered a major sin because it goes against the teachings of Islam that emphasize respect for elders and obedience towards them. Therefore, these three acts are considered some of the biggest sins according to Islamic teachings and should be avoided at all costs by Muslims.