Musnad Abu Ya'la al-Mawsili 6:5

Ibrahim ibn al-Hajjaj narrated to us, Abu 'Awanah narrated to us, from 'Abd al-Malik ibn 'Umayr, from Jabir ibn Samurah, who said: The people of Kufa complained about Sa'd to 'Umar, saying: "He does not know how to pray." Sa'd said: "As for me, I used to pray the prayer of the Messenger of Allah (peace be upon him) with them—my two night prayers—without omitting anything from them. I would prolong the first two [rak'ahs] and shorten the last two." 'Umar said: "That is what I thought of you, O Abu Ishaq." He sent men to ask about him in Kufa. They would not come to any mosque of the mosques of the people of Kufa without them saying good things or praising him, until they came to a mosque of the mosques of Banu 'Abs. A man called Abu Sa'dah said: "Since you have adjured us by Allah, he [Sa'd] used to not be just in judgment, nor divide equally, nor lead the military expeditions." Sa'd said: "O Allah, if he is a liar, then blind his sight, prolong his life, and expose him to trials." 'Abd al-Malik said: "I saw him afterwards, accosting slave girls in the alleys. When he was asked, 'How are you?' he would say: 'An old man, poor and tried; the supplication of Sa'd has struck me.'"