Musannaf Ibn Abi Shayba 37:549

Waki’ narrated to us, from Isma’il, from Qays, who said: Abu Sahla narrated to me that ‘Uthman said on the day of the House (ad-Dar): "Indeed, the Messenger of Allah (may Allah bless him and grant him peace) entrusted a covenant to me, and I am patient upon it." He said: And they used to think that it was that day.