Musnad Ahmad 3:9

Waki’ narrated to us, from Isma’il ibn Abi Khalid, who said: Qays said: Abu Sahlah narrated to me: That ‘Uthman said on the Day of the House (ad-Dar) when he was besieged: "Indeed, the Messenger of Allah (peace and blessings of Allah be upon him) entrusted a covenant to me, so I am patient regarding it." Qays said: And they used to consider it [to be] that day.