كتاب الصيام
13
The Book of Fasting
(38)
Chapter: The virtue of fasting Muharram
(38)
باب فَضْلِ صَوْمِ الْمُحَرَّمِ ‏

Abu Huraira (Allah be pleased with him) reported that he (the Messenger of Allah) was asked as to which prayer was most excellent after the prescribed prayer, and which fast was most excellent after the month of Ramadan. He said:

Prayer offered in the middle of the night and the most excellent fast after (fasting) in the month of Ramadan is the fast in God's month al-Muharram.
وَحَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا جَرِيرٌ، عَنْ عَبْدِ الْمَلِكِ بْنِ عُمَيْرٍ، عَنْ مُحَمَّدِ بْنِ، الْمُنْتَشِرِ عَنْ حُمَيْدِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ أَبِي هُرَيْرَةَ، - رضى الله عنه - يَرْفَعُهُ قَالَ سُئِلَ أَىُّ الصَّلاَةِ أَفْضَلُ بَعْدَ الْمَكْتُوبَةِ وَأَىُّ الصِّيَامِ أَفْضَلُ بَعْدَ شَهْرِ رَمَضَانَ فَقَالَ ‏ "‏ أَفْضَلُ الصَّلاَةِ بَعْدَ الصَّلاَةِ الْمَكْتُوبَةِ الصَّلاَةُ فِي جَوْفِ اللَّيْلِ وَأَفْضَلُ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ صِيَامُ شَهْرِ اللَّهِ الْمُحَرَّمِ ‏"‏ ‏.‏
Reference : Sahih Muslim 1163 b
In-book reference : Book 13, Hadith 262
USC-MSA web (English) reference : Book 6, Hadith 2612
  (deprecated numbering scheme)