Sahih Muslim 1157
Sahih Muslim · Book 13: The Book of Fasting · The Prophet's Fasts at times other than Ramadan; and it is recommended to ensure that no month is free of fasting
وَحَدَّثَنِيهِ عَلِيُّ بْنُ حُجْرٍ ، حَدَّثَنَا عَلِيُّ بْنُ مُسْهِرٍ ، ح وَحَدَّثَنِي إِبْرَاهِيمُ بْنُ مُوسَى ، أَخْبَرَنَا عِيسَى بْنُ يُونُسَ ، كِلاَهُمَا عَنْ عُثْمَانَ بْنِ حَكِيمٍ ، فِي هَذَا الإِسْنَادِ . بِمِثْلِهِ .
The same hadith as the previous hadith has been transmitted through another chain.