Aisha was asked about the fasting of the Prophet ﷺ. She said, "He would fast until we said he had committed to fasting, and he would break his fast until we said he had committed to not fasting. The Messenger of Allah ﷺ never fasted a complete month since he arrived in Medina except for Ramadan."
أخبرنا قتيبة قال حدثنا حماد عن أيوب عن عبد الله بن شقيق قال
عن صيام النبي ﷺ قالت كان يصوم حتى نقول قد صام ويفطر حتى نقول قد أفطر وما صام رسول الله ﷺ شهرا كاملا منذ قدم المدينة إلا 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 Qutayba, through him. It is also found in Al-Kubra, hadith no. 2658.