Musannaf Ibn Abi Shayba 27:411

Muhammad ibn al-Hasan al-Asadi narrated to us, he said: Ibrahim ibn Tahman narrated to us, from Musa ibn Uqbah, from his grandfather Abu Hasana, who said: I entered the house upon Uthman while he was besieged, and I heard Abu Hurayrah saying: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "You will surely encounter after me tribulation and disagreement." He said: A speaker said to him: "So what do you command us?" He said: "You must stick to the leader and his companions," and he struck the shoulder of Uthman.