Musnad Abu Ya'la al-Mawsili 150:407

Suwayd ibn Sa'id narrated to us, Muslim ibn Khalid narrated to us, from Tarif, from Yahya ibn Abi Kathir, from Abu Salamah, from Abu Hurayrah, that 'Aishah narrated to them that the Prophet, peace and blessings of Allah be upon him, used to fast all of Sha'ban. She said: I said, "O Messenger of Allah, is Sha'ban the most beloved of months to you to fast?" He said: "Indeed, Allah writes for every soul that is to die that year, so I love that my appointed time should come to me while I am fasting."