Musnad Ahmad 626:49

Isma'il narrated to us, Ayyub informed us, from Muhammad ibn Sirin, from 'Amr ibn Wahb al-Thaqafi, who said: We were with al-Mughirah ibn Shu'bah, and he was asked: "Did anyone from this nation lead the Prophet, peace and blessings of Allah be upon him, in prayer other than Abu Bakr?" He said: "Yes." He said: "And that increased his credibility with me, which is why I relate the hadith." He said: We were with the Prophet, peace and blessings of Allah be upon him, on a journey. When it was the time before dawn, he struck the neck of my riding beast, and I thought he had a need, so I turned aside with him. We went until we were out of sight of the people. He dismounted from his riding beast, then went off and disappeared from me until I could not see him. He stayed for a long time, then came and said: "Do you have a need, O Mughirah?" I said: "I have no need." He said: "Do you have water with you?" I said: "Yes." So I stood up to a water skin—or he said a leather water bag—hanging on the back of the saddle, and I brought it to him. I poured for him, and he washed his hands, and he washed them well. He said: And I am in doubt whether he said he rubbed them with dust or not. Then he washed his face. Then he went to uncover his arm, and he was wearing a Syrian cloak with tight sleeves, so it was tight, and he pulled his hands out from underneath it, and he washed his face and his hands. He said: The hadith mentions washing the face twice, and I do not know if it was like that or not. Then he wiped his forelock, wiped over his turban, and wiped over his leather socks. Then we rode until we caught up with the people, and the prayer had already been established. 'Abd al-Rahman ibn 'Awf had stepped forward to lead them, and he had already prayed one rak'ah with them, and they were in the second. I went to inform him, but he forbade me. So we prayed the rak'ah that we caught, and we completed the one we had missed.