Sayyiduna Anas bin Malik (may Allah be pleased with him) reported that the Prophet of Allah (peace and blessings be upon him) performed four Umrahs, all of them in Dhu al-Qa'dah except the Umrah that he performed with his Hajj: one Umrah in the year of al-Hudaybiyah in Dhu al-Qa'dah, one Umrah the following year in Dhu al-Qa'dah, one Umrah from al-Ji'ranah when he distributed the spoils of Hunayn, also in Dhu al-Qa'dah, and one Umrah with his Hajj.
Sayyiduna Anas (may Allah be pleased with him) says this only on the basis of his view that he (peace and blessings be upon him) performed Hajj al-Qiran. It has also been narrated from people other than Sayyiduna Anas bin Malik (may Allah be pleased with him), but whether it is established is open to question.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8834