By Allah, the Messenger of Allah ﷺ never fasted a complete month other than Ramadan. When he fasted, he would continue fasting until one would say, "By Allah, he will not break his fast." And when he stopped fasting, he would continue without fasting until one would say, "By Allah, he will not fast."
حدثنا يحيى بن حماد قال أخبرنا أبو عوانة عن أبي بشر عن سعيد بن جبير
والله ما صام رسول الله ﷺ شهرا كاملا قط غير رمضان وكان إذا صام صام حتى يقول القائل والله لا يفطر ويفطر حتى إذا أفطر يقول القائل والله لا يصوم
Its isnad is sahih. Yahya bin Hammad bin Abu Ziyad Shaybani is trustworthy, one of the teachers of Ahmad and Bukhari. Ibn Saad and Abu Hatim and others confirmed his trustworthiness, and Ajli said, "A Basran, trustworthy, and he was one of the people who transmitted the most from Abu Awana."The hadith is a repetition of 2450.