During his Caliphate it was the usual practice of Umar that he would patrol the streets and suburbs of Madina to watch the interests of the people, and attend to their needs.

One night, Umar as usual went in disguise with his comrade Ibn Abbas to see the condition of the people. They strolled from one quarter to another. At last they came to a colony where very poor people lived.
While passing by a small hutment, the Caliph heard a whispering talk within. The mother was telling her daughter that the amount fetched by her that day on account of the sale of milk was very little. She told her that when she was young, and used to sell milk, she always mixed water with milk, and that led to considerable profit. She advised her daughter to do the same.
The girl said, "You adulterated milk, when you were not a Muslim. Now that we are Muslims, we cannot adulterate milk."
The mother said that Islam did not stand in the way of he adulteration of milk.
The daughter said, "Have you forgotten the Caliph's order? He wants that the milk should not be adulterated."
The mother said, "But the Caliph has forgotten us. Were so poor, what else should we do but adulterate milk in order to win bread?"
The daughter said "Such a bread would not be lawful, and as a Muslim I would not do anything which is against he orders of the Caliph, and whereby other Muslims are deceived."
The mother said, "But there is neither the Caliph nor any of his officers here to see what we do. Daughter you are still a child. Go to bed now and tomorrow I will myself mix the milk with water for you."
The girl refused to fall in with the plan of her mother. She said, "Caliph may or may not be here, but his order is order, and it must be obeyed. My conscience is My Caliph. You may escape the notice of the Caliph and his officers, but how can we escape the notice of Allah and our own conscience?"
Thereupon the mother remained quiet. The lamp was extinguished and the mother and the daughter went to sleep.
The next day, Umar sent a man to purchase milk from the girl. The milk was unadulterated. The girl had kept her resolve.
Umar turned to his companion and said, "The girl has kept her resolve in spite of the exhortation of her mother. She deserves a reward. What reward should I give her?"

"She should be paid some money" said Ibn Abbas.
Umar said, 'Such a girl would become a great mother Her integrity is not to be weighed with a few coins; it is to be measured in the scale of national values. I shall offer her the highest award in my gift, and which shall also be in the highest interest of the nation."

The Caliph summoned the daughter and the mother to his court. The mother trembled as she stood before the mighty ruler. But the girl faced the Caliph boldly and with great equanimity.

Then before the gathering, Umar related how he had overheard the mother and the daughter, and how in spite of the exhortations of the mother the daughter had kept he resolve.
Someone suggested that the mother should be taken the task. The Caliph said that ordinarily he would have punished the mother, but he had forgiven her for the sake of he daughter. Turning to the girl the great Caliph said, "Islam needs daughters like you, and as a Caliph of Islam it devolve on me to reward you by owning you as a daughter".
The Caliph called his sons, and addressing them said "Here is a gem of a girl who would make a great mother. I desire that one of you should take this girl as wife. I know of no better bride than this girl of sterling character. In matters of wedlock, it should be the character, and not the stature in life that should count."
Abdullah and Abdur Rahman the elder sons of the Caliph were already married. Asim the third son was yet unmarried, and he offered to marry the girl. Thereupon with the consent of the milkmaid and her mother Asim was married to the girl, and the milkmaid became the daughter-in-law of the Caliph.
From this union was born a daughter Umm Asim, who became in due course the mother of Umar bin Abdul Aziz. Umar bin Abdul Aziz became a Caliph in due course.
While other Caliphs of the Ummayad dynasty reveled in luxury, Umar bin Abdul Aziz as a Caliph set up standards for austerity and simplicity following in the footsteps of Umar the second Caliph of Islam. It is said that if ever there was a noble Caliph after the 'Rightly guided Caliphs', such a man was Umar bin Abdul Aziz. And he inherited the noble qualities of the milkmaid who married the Caliph's son, and those of Umar Farooq who had the eye to discern the nobler qualities of sterling character in a poor girl.

Abu Hafsa "Abdulmalik Clare" - Blind Hearts