Musnad Ahmad 1153:1218

Husayn ibn Ali narrated to us, from Za'idah, from Layth, from Mujahid, from Aisha, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "When the sins of the servant become numerous, and he does not have deeds to expiate them, Allah, the Exalted and Majestic, afflicts him with sorrow to expiate them from him."