Musannaf Ibn Abi Shayba 3:2422

Abu Usama narrated to us, from Musawir, who said: Hilal ibn Abi Humayd narrated to us, saying: I used to prompt Abdullah ibn Hakim when he would falter in prayer. So he said to me one day: "Did you not pray with us?" I said: "No." He said: "I complained of that; I hesitated last night and did not find anyone to prompt me."