Sayyiduna Urwah bin Mudarris (may Allah be pleased with him) said: I saw the Messenger of Allah (peace and blessings be upon him) standing at Muzdalifah, and he (peace and blessings be upon him) said: "Whoever prays this prayer of ours, then departs with us, having already stood at Arafah before that, by night or by day, his Hajj is complete."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14454