Sahih al-Bukhari 4253, 4254

It is related that Mujahid said, "'Urwa ibn az-Zubayr and I entered the mosque and found 'Abdullah ibn 'Umar sitting next to the room of 'A'isha. He said, 'How many times did the Prophet, may Allah bless him and grant him peace, do 'umra?' He said, 'Four times: once in Rajab.' We heard 'A'isha, Umm al-Mu'minin, cleaning her teeth and so 'Urwa said, 'O Umm al-Mu'minin! Do you not hear what Abu 'Abdu'r-Rahman is saying? He says that the Messenger of Allah, may Allah bless him and grant him peace, went on 'umra four times, one of which was in Rajab.' She said, 'The Prophet, may Allah bless him and grant him peace, did not do any 'umra but that he was present with him. He never went on 'umra in Rajab.'"