It was narrated from Qutaadah that Anas (may Allaah be pleased with him) told him that the Messenger of Allaah (peace and blessings of Allaah be upon him) performed Umrah four times, all of them in Dhu'l-Qi'dah apart from the Umrah which he performed with his Hajj: (he did) Umrah from al-Hudaybiyah or at the time of al-Hudaybiyah in Dhu'l-Qi'dah; (he did) Umrah the following year in Dhu'l-Qi'dah; and (he did) Umrah from Ja'raanah when he shared out the booty of Hunayn in Dhu'l-Qi'dah.
Narrated by al-Bukhaari, al-Hajj, 1654; Muslim, al-Hajj, 1253
Ibn al-Qayyim said:
He did Umrah four times after the Hijrah, four Umrahs, all of them in Dhu'l-Qi'dah.
The first was the Umrah of al-Hudaybiyah, which was the first of them, in 6 AH, but the mushrikeen prevented him from reaching the House (the Ka'bah), so he offered the sacrifice (of camels) when his way was blocked at al-Hudaybiyah, and he and his companions shaved their heads and exited the state of ihraam, and went back in the same year to Madeenah.
The second was the Fulfilled Umrah in the following year, when he entered Makkah and stayed there for three (days), then he left after completing his Umrah.
The third was the Umrah which he did along with his Hajj.
The fourth was his Umrah from al-Ja'raanah, when he went out to Hunayn then he came back to Makkah and performed Umrah from al-Ja'raanah.
He said: there is no (scholarly) dispute concerning the fact that he did no more than four Umrahs.
See Zaad al-Ma'aad, vol. 2, p. 90-93
The scholars said: the Prophet (peace and blessings of Allaah be upon him) performed these Umrahs in Dhu'l-Qid'ah because of the virtue of this month and in order to go against the (ways of) Jaahiliyyah, because they used to think that this (i.e., doing Umrah in Dhu'l-Qi'dah) was one of the most evil of evil actions, as stated above. So the Prophet (peace and blessings of Allaah be upon him) did that several times in this month as this was the most eloquent way of explaining that it was permissible and of demonstrating the beliefs of Jaahiliyyah to be false.
And Allaah knows best.
Sharh Muslim, 8/235
Reproduced from Islam QA