Urwah bin Zubair (may Allah have mercy on him) asked Sayyiduna Ibn Umar (may Allah be pleased with them both) whether the Prophet (peace and blessings be upon him) performed Umrah in the month of Rajab. He replied, "Yes!" Urwah conveyed this to Sayyidah Aisha (may Allah be pleased with her), so she said: "May Allah have mercy on Abu Abdur Rahman. The Prophet (peace and blessings be upon him) performed every Umrah that he (Ibn Umar) participated in with him (the Prophet), (but he forgot that) the Prophet (peace and blessings be upon him) never performed Umrah in the month of Rajab."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5416
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ : 1777، م :1255.