The Book of Fasting
13/34. Chapter:
The Prophet's Fasts at times other than Ramadan; and it is recommended to ensure that no month is free of fasting
Sahih Muslim
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، ح وَحَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا عُثْمَانُ بْنُ حَكِيمٍ الأَنْصَارِيُّ، قَالَ سَأَلْتُ سَعِيدَ بْنَ جُبَيْرٍ عَنْ صَوْمِ، رَجَبٍ - وَنَحْنُ يَوْمَئِذٍ فِي رَجَبٍ - فَقَالَ سَمِعْتُ ابْنَ عَبَّاسٍ - رضى الله عنهما - يَقُولُ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَصُومُ حَتَّى نَقُولَ لاَ يُفْطِرُ . وَيُفْطِرُ حَتَّى نَقُولَ لاَ يَصُومُ .
'Uthman b. Hakim al-Ansari said: I asked Sa'id b. Jubair about fasting In Rajab, and we were then passing through the month of Rajab, whereupon he said: I heard Ibn 'Abbas (Allah be pleased with both of them) as saying: The Messenger of Allah (ﷺ) used to observe fast (so continuously) that we (were inclined) to say that he would not break (them) and did not observe them so conti- nuously) that we (were inclined to say) that he would not observe fast.
Reference : Sahih Muslim 1157cIn-book reference : Book 13, Hadith 232USC-MSA web (English) reference : Book 6, Hadith 2585