Musnad Ahmad 3:88

'Affan narrated to us, Abu 'Awanah narrated to us, from Ibrahim ibn al-Muhajir, from 'Ikrimah ibn Khalid, a man from the people of Medina narrated to me: That the mu'adhdhin gave the adhan for the 'Asr prayer. He said: So 'Uthman called for water for purification and performed purification. He said: Then he said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever purifies himself as he was commanded, and prays as he was commanded, his sins will be expiated." Four of the companions of the Messenger of Allah, peace and blessings of Allah be upon him, bore witness to that. He said: So they testified to him regarding that on the authority of the Prophet, peace and blessings of Allah be upon him.