Musnad Ahmad 3:80

Abu al-Mughirah narrated to us, al-Awza'i narrated to us, Yahya ibn Abi Kathir narrated to us, from Muhammad ibn Ibrahim al-Taymi, Shaqiq ibn Salamah narrated to me, from Humran, who said: Uthman was sitting on the seats, and he called for water for ablution. He performed ablution, then said: "I saw the Messenger of Allah, peace and blessings of Allah be upon him, perform ablution in this seat of mine, then he said: 'Whoever performs ablution like this ablution of mine, then stands and prays two rak'ahs, his past sins will be forgiven for him.'" And the Messenger of Allah, peace and blessings of Allah be upon him, said: "Do not be deceived."