Musannaf Ibn Abi Shayba 3:5268

Waki' narrated to us, Hisham bin 'Urwah narrated to us, from his father, from Humran bin Aban, from 'Uthman bin 'Affan, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There is no man who performs ablution and perfects the ablution, then prays, except that what is between him and the other prayer is forgiven for him."