Mujahid (may Allah have mercy on him) said: The Messenger of Allah (peace and blessings be upon him) performed three Umrahs, all of them in Dhu al-Qa'dah. Among them is the Umrah in which the sacrificial animals were prevented; the Messenger of Allah (peace and blessings be upon him) sent messages to the people of Makkah, and they made peace with him on the condition that he would turn back from them that year. He said: So the Messenger of Allah (peace and blessings be upon him) slaughtered the sacrificial animals at al-Hudaybiyah, where he had camped by the tree, and then went back.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10086