Musnad Ahmad 30:1421

'Affan narrated to us, Wuhayb narrated to us, Musa ibn 'Uqbah narrated to us, he said: My grandfather, the father of my mother, Abu Habibah, narrated to me that he entered the house while 'Uthman was besieged therein, and that he heard Abu Hurayrah asking 'Uthman for permission to speak, so he granted it to him. He stood up, praised Allah, and extolled Him, then said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: 'You will encounter after me a tribulation and a disagreement,' or he said: 'a disagreement and a tribulation.'" A speaker among the people said to him: "Then who is for us, O Messenger of Allah?" He said: "You must follow the Trustworthy One and his companions," and he was pointing to 'Uthman by that.