Abu Sahla says that on the day when Sayyiduna Uthman (may Allah be pleased with him) was besieged, which became famous as "Yawm al-Dar," he said that the Messenger of Allah (peace and blessings be upon him) took a covenant from me, and I am steadfast and firm upon it.
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 501