Musnad Abu Ya'la al-Mawsili 42:160

'Abd al-A'la narrated to us, Hammad narrated to us, from Bishr ibn Harb, from Abu Sa'id al-Khudri: That the Messenger of Allah (may Allah bless him and grant him peace) forbade continuous fasting (al-wisal). Abu Sa'id said: "This sister of mine is fasting continuously, and I forbid her, but she refuses."