Sayyiduna Urwah bin Mudarris (may Allah be pleased with him) said: I came to the Messenger of Allah (peace and blessings be upon him) at Muzdalifah and said: "O Messenger of Allah! Is my Hajj valid?" He (peace and blessings be upon him) said: "Whoever prays this prayer with us in this place, having already departed from Arafat before that, by night or by day, his Hajj is complete and he has fulfilled his rites (of removing his dishevelment)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14465