Salim bin Abdullah bin Umar (may Allah have mercy on him) narrates from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him): "Whoever reaches the Night of Sacrifice before the dawn rises has attained the Hajj, and whoever does not stand (at Arafah) before the morning has missed the Hajj; it could not be done."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9818