Musnad Ahmad 1153:2106

'Abd al-Samad narrated to us, he said: My father narrated to me, Yazid—meaning al-Rishk—narrated to us, from Mu'adhah, who said: A woman asked 'Aishah, while I was a witness, about the continuous fasting of the Messenger of Allah, peace and blessings of Allah be upon him. She said to her: "Do you act as he acted? For indeed, his past and future sins had been forgiven for him, and his action was a supererogatory act for him."