Narrated Ibn `Abbas: The Prophet never fasted a full month except the month of Ramadan, and he used to fast till one could say, "By Allah, he will never stop fasting," and he would abandon fasting till one would say, "By Allah, he will never fast."
Hadith Referenceصحيح البخاري / كتاب الصوم / 1971
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة