It is narrated from Sayyiduna Mughirah bin Shu'bah (may Allah be pleased with him); he said: We were with the Prophet (peace and blessings be upon him) on a journey. When it was the time of suhur (before dawn), I urged my mount on and went forward with him (peace and blessings be upon him). He (peace and blessings be upon him) went off until he disappeared from my sight, then came back and said: "Do you need anything?" I said: I have no need. He (peace and blessings be upon him) said: "Do you have water with you?" I said: Yes. So he (peace and blessings be upon him) performed ablution and wiped over his leather socks, then went on until he reached the people while they were praying, and Abd al-Rahman bin Awf (may Allah be pleased with him) was leading them. At the arrival of the Messenger of Allah (peace and blessings be upon him), he (Abd al-Rahman (may Allah be pleased with him)) moved (to step back), so he (peace and blessings be upon him) signalled with his hand to Abd al-Rahman to stay where he was (and continue the prayer). So we prayed what we caught, and we completed what we had missed.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18157