Anas said that God’s messenger performed the 'umra four times, each of them Dhul Qa'da except the one which was combined with his hajja, one from al-Hudaibiya in Dhul Qa'da, one in the following year in Dhul Qa'da, one from al-Ji'rana where he divided the spoils of Hunain (The battle in which the Prophet defeated Hawazin after the conquest of Mecca in 8 A.H) in Dhul Qa'da, and one along with his hajja.
Bukhari and Muslim.