The Messenger of Allah ﷺ as saying: The most excellent fast after Ramadan is Allah's month al-Muharram, and the most excellent prayer after the prescribed prayer is the prayer during night.  

قَالَ رَسُولُ اللَّهِ ﷺ أَفْضَلُ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ شَهْرُ اللَّهِ الْمُحَرَّمُ وَإِنَّ أَفْضَلَ الصَّلاَةِ بَعْدَ الْمَفْرُوضَةِ صَلاَةٌ مِنَ اللَّيْلِ لَمْ يَقُلْ قُتَيْبَةُ شَهْرِ قَالَ رَمَضَانَ