عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: سُئِلَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ أَيُّ الصَّلَاةِ أَفْضَلُ بَعْدَ الْمَكْتُوبَةِ؟ قَالَ: ((الصَّلَاةُ فِي جَوْفِ اللَّيْلِ))، قِيلَ: أَيُّ الصِّيَامِ أَفْضَلُ بَعْدَ رَمَضَانَ؟ قَالَ: ((شَهْرُ اللَّهِ الَّذِي تَدْعُونَهُ الْمُحَرَّمَ))
It is narrated from Sayyiduna Abu Huraira, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, was asked: "Which prayer is the best after the obligatory prayers?" He, peace and blessings be upon him, replied: "Prayer at any time during the night." Then someone asked: "Which fasts are the best after those of Ramadan?" He, peace and blessings be upon him, replied: "The fasts of Allah’s month, which you call Muharram."