Musnad Ahmad 626:60

Yazid ibn Harun narrated to us, Ibn 'Awn informed us, from al-Sha'bi, from 'Urwah ibn al-Mughirah ibn Shu'bah, from his father, and from Ibn Sirin, who attributed it to al-Mughirah ibn Shu'bah, who said: We were with the Prophet, peace and blessings of Allah be upon him, and he nudged my back, or my shoulder, with something he had with him. He said: I followed him, and the Messenger of Allah, peace and blessings of Allah be upon him, relieved himself, then he came and said: "Do you have water?" I said: "Yes," and I had a small water skin with me. He washed his face, and he was wearing a Syrian jubbah (outer garment) with tight sleeves. He inserted his hand and lifted the jubbah onto his shoulders, and brought his hands out from beneath the jubbah, and washed his forearms, and wiped over his turban. He mentioned the forelock with something, and wiped over his leather socks. Then we approached and caught up with the people during the morning prayer, and 'Abd al-Rahman was leading them in prayer, and they had already prayed one rak'ah. I went to inform him, but he forbade me. So we prayed one rak'ah with him, and we completed the one we had missed.