Musnad Abu Ya'la al-Mawsili 210:7

Yahya ibn Ayyub narrated to us, Shu'ayb ibn Harb narrated to us, Shayban Abu Mu'awiyah narrated to us, Abu Ya'fur al-'Abdi narrated to us, from 'Abdullah ibn Abi Sa'id, from Hafsah, that the Prophet, peace and blessings of Allah be upon him, said regarding 'Uthman: "Should I not be shy of a man whom the angels are shy of?"