And this is not an exception. It proved to be the general rule. Waleed bin Yazid bin Abdul Malik was another Caliph from Bani Umayya. He was a drunkard. One night he was drinking with one of his concubines, till they heard the A'dhaan of the prayer of Fajr (dawn). He swore that the concubine would lead in the prayer. So she wore the robe of the Caliph and led in the prayer in the same condition of drunkenness.
One day he saw his teenage unmarried daughter and molested her sexually. Her servant woman was sitting there. She said that (it was not Islam) it was the religion of Majus. Waleed replied her that: "A man who cares for the tongues of people, dies in sorrow; and the daring man gets all the pleasures."
Harun Rashid, the famous Caliph of "One thousand and one nights," who is thought one of the greatest Caliphs, wanted io sleep with a concubine of his late father. The concubine said that it was not possible because she was like his mother. Harun Rashid called Qadhi Abu Yusuf and told him to find a way to satisfy his lust. The Qadhi said: "She is just a slave girl. Should you accept whatever she says? No. Do not accept her words as true."
So the Caliph satisfied his desire. Ibn Mubarak comment: "I do not know who among these three was more surprising: the Caliph who put his hand into the blood and property of the Muslims and did not respect his step-mother; Or the slave girl who refused to satisfy the desire of the Caliph; Or the Qadhi who allowed the Caliph to dishonour his father and sleep with that concubine who was his stepmother."