Sayyiduna Abu Bakrah (may Allah be pleased with him) says: The Prophet (peace and blessings be upon him) addressed us on the Day of Sacrifice and said: "What day is this?" We said: Allah and His Messenger (peace and blessings be upon him) know best. He (peace and blessings be upon him) remained silent until we thought he would give it some new name. Then he (peace and blessings be upon him) said: "Is it not the Day of Sacrifice?" We said: Certainly. He (peace and blessings be upon him) said: "What month is this?" We said: Allah and His Messenger (peace and blessings be upon him) know best. He (peace and blessings be upon him) remained silent until we thought he might give it some new name. He (peace and blessings be upon him) said: "Is it not Dhu al-Hijjah?" We said: Certainly. He (peace and blessings be upon him) said: "What city is this?" We said: Allah and His Messenger (peace and blessings be upon him) know best. He (peace and blessings be upon him) remained silent until we thought he (peace and blessings be upon him) would give it some other name. He (peace and blessings be upon him) said: "Is it not the sacred city?" We said: Certainly. He (peace and blessings be upon him) said: "Your blood is sacred, like the sanctity of this day of yours, in this month of yours, in this city of yours. O Allah, have I conveyed?" They said: Yes! Then he (peace and blessings be upon him) said: "Let whoever of you is present convey it to whoever is absent, for many a person to whom something is conveyed retains it better than the one who heard it. Beware! Do not become disbelievers after me, striking one another's necks."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9614