Sayyiduna Abd al-Rahman bin Ya'mar al-Dili (may Allah be pleased with him) says: I came to the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was at Arafat. A group of the Companions (may Allah be pleased with them) came to him, and they instructed a man, who called out: "O Messenger of Allah, how is the Hajj?" He (peace and blessings be upon him) ordered a man to announce: "Hajj is the Day of Arafah. Whoever comes before the Fajr prayer of the night of Jam' (Muzdalifah), his Hajj is complete. The days of (staying at) Mina are three. Whoever hastens (in stoning) in two days, there is no sin upon him." Then he seated a man behind him (on his mount), and he announced this.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9813