The Messenger of Allah ﷺ performed four Umrahs, all of them in Dhul-Qadah, except the one he performed together with his Hajj.
حدثنا أبو الوليد الطيالسي وهدبة بن خالد قالا حدثنا همام عن قتادة
أن رسول الله ﷺ اعتمر أربع عمر كلهن في ذي القعدة إلا التي مع حجته
Muslim narrated it in the Book of Hajj, in the chapter on the number of times the Prophet ﷺ performed Umrah and their timing, Hadith 1253, from the hadith of Hudba bin Khalid. Bukhari narrated it in the Book of Umrah, in the chapter on how many times the Prophet performed Umrah, Hadith 1778, from the hadith of Hammam, with the same wording.