Sayyiduna Urwah bin Mudarris (may Allah be pleased with him) says: I came to the Messenger of Allah (peace and blessings be upon him) at Muzdalifah and said: O Messenger of Allah! I have come from the two mountains of Tayyi'. By Allah! I have come having exhausted myself and my mount as well. I did not leave any mountain without standing upon it. Is there a Hajj for me? He (peace and blessings be upon him) said: "Whoever is present with us in the Fajr prayer at Muzdalifah, and had performed the standing at Arafah before that during part of the day or the night, his Hajj is complete and he has completed (the removal of) his dishevelment." Sufyan says that Zakariyya added something to it, and he was the one of the three who best remembered this hadith. He said: I said: O Messenger of Allah! I have come at this hour from the mountains of Tayyi'. I have worn out my mount and exhausted myself as well; is there a Hajj for me? He (peace and blessings be upon him) said: "Whoever is present with us in this prayer, and stands with us until he departs, and had stood at Arafah before that during part of the night or the day, his Hajj is complete and his dishevelment is removed." Sufyan says that Dawud bin Abi Hind added: I came to the Messenger of Allah (peace and blessings be upon him) when the dawn broke.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9814