It is narrated from Hasan al-Basri (may Allah have mercy on him) that Sayyiduna Uthman bin Abi al-As (may Allah be pleased with him) married one of the wives of Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), and he said: By Allah, when I married her, I did not marry her out of desire for wealth or children; rather, I wanted her to tell me about the nights of Sayyiduna Umar (may Allah be pleased with him). So he asked her: How was the night prayer of Sayyiduna Umar (may Allah be pleased with him)? She said: He would pray the Isha prayer, then order us to place a vessel of water by his head and cover it. When he woke (from sleep) during the night, he would put his hand in the water and wipe his face and hands, then remember Allah Almighty for as long as he wished, then he would wake (from sleep) again and again until the time came at which he would stand for his (tahajjud) prayer. Then Ibn Buraydah said to him: Who told you this? He said: The daughter of Uthman bin Abi al-As told me. He said: By Allah, she is trustworthy.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8303