Musannaf Ibn Abi Shayba 1:2085

Waki’ narrated to us, from Mis’ar, from Abu Sakhra Jami’ ibn Shaddad, who said: I heard Humran ibn Aban, the freed slave of Uthman ibn Affan, saying: I used to place the water for Uthman’s purification for him, and there did not come upon him a day except that he would pour a drop of water over himself during it.