Musnad Ahmad 1153:1219

Husayn ibn Ali narrated to us, from Za'idah, from Hisham, from Ibn Sirin, who said: Abdullah ibn Shaqiq narrated to me, from Aisha, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) did not fast a complete month since he arrived in Medina, except for Ramadan."