Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrated that, except for Ramadan, the Prophet Muhammad (peace and blessings be upon him) never fasted for an entire month. When he began to observe voluntary fasts, an onlooker would say, "By Allah, he will not stop fasting now." And similarly, when he stopped keeping voluntary fasts, an onlooker would say, "By Allah, he will not fast now."
Hadith Referenceاللؤلؤ والمرجان / كتاب الصيام / 713
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 30 كتاب الصوم: 53 باب ما يذكر في صوم النبي صلی اللہ علیہ وسلم وإفطاره»