(34) بَاب صِيَامِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي غَيْرِ رَمَضَانَ وَاسْتِحْبَابِ أَنْ لَا يُخْلِيَ شَهْرًا عَنْ صَوْمٍ
This hadith has been narrated on the authority of Abu Bishr with the same chain of transmitters (with a slight variation of words and these are), that he (the narrator) said:
" During any month continuously since he came to Medina."
Reference: Sahih Muslim 1157 b
In-book reference: Book 13, Hadith 231
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2584