(34) بَاب صِيَامِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي غَيْرِ رَمَضَانَ وَاسْتِحْبَابِ أَنْ لَا يُخْلِيَ شَهْرًا عَنْ صَوْمٍ
A hadith like this has been narrated on the authority of Abdullah b. Shaqiq but in the chain of transmitters no mention is made of Hisham and Muhammad.
Reference: Sahih Muslim 1156 d
In-book reference: Book 13, Hadith 226
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2579