Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) said: "Whoever departs from Arafat before the morning, his Hajj is complete; and whoever misses the standing at Arafah has missed the Hajj."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9815