I will be harsh and stern against the aggressor, but I will be a pillar of strength for the weak. I will not calm down until I will put one cheek of a tyrant on the ground and the other under my feet, and for the poor and weak, I will put my cheek on the ground.
Remember, I have not appointed you as commanders and tyrants over the people. I have sent you as leaders instead, so that the people may follow your example. Give the Muslims their rights and do not beat them lest they become abused. Do not praise them unduly, lest they fall into the error of conceit. Do not keep your doors shut in their faces, lest the more powerful of them eat up the weaker ones. And do not behave as if you were superior to them, for that is tyranny over them.
As quoted in Omar the Great : The Second Caliph Of Islam (1962) by Muhammad Shibli Numani, Vol. 2, p. 33
I know that you are just a stone and that you can neither do any harm nor give benefit. Had I not seen Messenger of Allah (peace and blessings of Allâh be upon him) kissing you, I would not have kissed you.
Yet the abstinence and humility of Omar were not inferior to the virtues of Abubeker: his food consisted of barley bread or dates; his drink was water; he preached in a gown that was torn or tattered in twelve places; and the Persian satrap, who paid his homage to the conqueror, found him asleep among the beggars on the steps of the mosch of Medina.
Muhammad ibn Umar Waqidi and others have said, “Umar asked Ali for the hand of his daughter, Umm Kulthum, in marriage. Ali replied that she had not yet attained the age (of puberty).”Umar replied: “By Allah, this is not true. You do not want her to marry me. If she is underage, send her to me.” Thus, Ali called Umm Kulthum, they prepared her and made her up. Then he asked for a piece of cloth which he folded and handed over to Umm Kulthum telling her to take the garment to Amirul Mu‘meneen and tell him: “My father has sent me to you instructing me to convey you his greetings and said that if you liked the garment, take it or else, return it!” When Umm Kulthum went to Umar, the latter said: “May Allah bless you and your father, I like it.” Umm Kulthum returned to his father and said: “He did not unfold the garment, but just looked at me!” Then Ali married her to Umar and she bore him a child named Zaid.
Muhammad ibn Saad, Kitab al-Tabaqat al-Kabir Volume 8, p. 299-300. Translated by Bewley, A. (1995). The Women of Madina. London: Ta-Ha Publishers.