Musannaf Ibn Abi Shayba 37:597

Yazid ibn Harun narrated to us, he said: Abu Ubaydah al-Naji informed us, from al-Hasan, he said: The Ansar came to Uthman and said: "O Commander of the Faithful, we shall aid Allah twice; we aided the Messenger of Allah (may Allah bless him and grant him peace), and we shall aid you." He said: "There is no need for that; return." And al-Hasan said: "By Allah, if they had wanted to protect him with their cloaks, they would have protected him."