Sayyiduna al-Mughirah bin Shu'bah (may Allah be pleased with him) says that he travelled with the Prophet (peace and blessings be upon him) in the Battle of Tabuk. When dawn drew near, he (peace and blessings be upon him) turned aside, and I turned aside with him. He (peace and blessings be upon him) made his mount kneel and went off, and I had a vessel of water with me. When the Messenger of Allah (peace and blessings be upon him) came, he instructed me, and I poured water from the vessel over his (peace and blessings be upon him) hands three times. Then he (peace and blessings be upon him) washed his face. Then he (peace and blessings be upon him) was bringing his forearms out of the jubbah, and when the sleeves of the jubbah were too narrow, he (peace and blessings be upon him) took his hands out from beneath the jubbah and washed them up to the elbows. Then he wiped over his head and his leather socks and completed the ablution. Then he came back, and al-Mughirah (may Allah be pleased with him) was with him (peace and blessings be upon him). He (peace and blessings be upon him) found the people in prayer, with Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) leading them. Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) had led them in one rak'ah of Fajr before the Messenger of Allah (peace and blessings be upon him) arrived. The Prophet (peace and blessings be upon him) came and lined up with the people behind Sayyiduna Abd al-Rahman bin Awf (may Allah be pleased with him) in the second rak'ah. When Sayyiduna Abd al-Rahman (may Allah be pleased with him) ended with salam, the Prophet (peace and blessings be upon him) stood up and completed his prayer. The people were alarmed at this and began saying 'Subhan Allah' a great deal. When the Prophet (peace and blessings be upon him) completed the prayer, he said: "You have done right," or he said: "You have done well."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5308