I asked her about the fasting of the Messenger of Allah ﷺ. She said, "The Messenger of Allah ﷺ used to fast until we would say he is fasting continuously, and he would refrain from fasting until we would say he is no longer fasting. He never fasted a complete month since coming to Medina, except for Ramadan."
أخبرنا محمد بن أحمد بن أبي يوسف الصيدلاني حراني قال حدثنا محمد بن سلمة عن هشام عن ابن سيرين عن عبد الله بن شقيق
سألتها عن صيام رسول الله ﷺ قالت كان رسول الله ﷺ يصوم حتى نقول قد صام ويفطر حتى نقول قد أفطر ولم يصم شهرا تاما منذ أتى المدينة إلا أن يكون رمضان
Muslim narrated it in the Book of Fasting, chapter on the Prophet's ﷺ fasting outside of Ramadan, etc., hadith no. 1156/174, from the hadith of Hisham bin Hassan with this wording, and it is also in Al-Kubra, hadith no. 2493.