Musannaf Ibn Abi Shayba 1:2044

Abu Bakr narrated to us, he said: Abu Usamah narrated to us, from Ali ibn Mas'adah, he said: Abdullah al-Rumi narrated to us, he said: Uthman used to stand at night and perform his own ablution himself. It was said to him: "If only you would order some of the servants [to do it for you]." He said: "I like to perform it myself."