Musannaf Ibn Abi Shayba 21:738

Abu Khalid al-Ahmar narrated to us, from Hajjaj, from Yahya ibn Abi Kathir, from Urwah, from Aisha, who said: I was beside the Prophet, may Allah bless him and grant him peace, and I missed him, so I followed him. Suddenly, he was at al-Baqi, raising his hands and supplicating. He said: "O daughter of Abu Bakr, did you think that Allah and His Messenger would treat you unjustly? Indeed, Allah descends on this night, the middle of Sha'ban, and He forgives therein of sins more than the number of hairs on the goats of Kalb."