Mu'adhah (a woman of that name) narrates: A woman asked Sayyidah Aishah (may Allah be pleased with her), and I was present there at the time. That woman asked about the continuous fasting (sawm al-wisal) of the Prophet (peace and blessings be upon him). Sayyidah Aishah (may Allah be pleased with her) said to her: "Do you want to act as the Prophet (peace and blessings be upon him) acted? His past and future sins have already been forgiven, and his deeds were voluntary (extra) for him."
Ahmad recorded it, and its narrators are the narrators of the Sahih; part of it is reported in the Sahih.