Sayyiduna Ibn Umar (may Allah be pleased with them both) was sitting reclining against the chamber of Aishah (may Allah be pleased with her), when he was asked: In which month did the Messenger of Allah (peace and blessings be upon him) perform Umrah? He said: "In Rajab."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13478