Musnad Ahmad 3:86

'Affan narrated to us, Abu 'Awanah narrated to us, from 'Asim, from al-Musayyib, from Musa ibn Talhah, from Humran, who said: 'Uthman used to perform ghusl once every day since he accepted Islam. One day, I placed water for his ablution for prayer. When he performed ablution, he said: "I intended to tell you a hadith I heard from the Messenger of Allah, may Allah bless him and grant him peace." Then he said: "It occurred to me not to tell it to you." Al-Hakam ibn Abi al-'As said: "O Commander of the Faithful, if it is good, we will take it, and if it is evil, we will avoid it." He said: So he said: "I will tell it to you: The Messenger of Allah, may Allah bless him and grant him peace, performed ablution like this ablution, then said: 'Whoever performs this ablution, and performs the ablution well, then stands for prayer and completes its bowing and prostration, it will expiate for what is between it and the other prayer, as long as he does not commit a maqtal,'" meaning: a major sin.