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. (Using translation from Abū Dāʾūd 2429)   

قَالَ رَسُولُ اللهِ ﷺ أَفْضَلُ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ شَهْرُ اللهِ الْمُحَرَّمُ وَإِنَّ أَفْضَلَ الصَّلَاةِ بَعْدَ الْمَفْرُوضَةِ صَلَاةٌ مِنَ اللَّيْلِ لَمْ يَقُلْ قُتَيْبَةُ شَهْرُ قَالَ رَمَضَانُ  

[Machine] The Messenger of Allah ﷺ said, "The best fasting after Ramadan is the fasting in the month of Allah, which you call Muharram, and the best prayer after the obligatory prayer is the prayer in the middle of the night. And likewise..."  

قَالَ رَسُولُ اللهِ ﷺ أَفْضَلُ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ شَهْرُ اللهِ الَّذِي تَدْعُونَهُ الْمُحَرَّمَ وَأَفْضَلُ الصَّلَاةِ بَعْدَ الْمَفْرُوضَةِ الصَّلَاةُ فِي جَوْفِ اللَّيْلِ وَكَذَلِكَ  

[Machine] The Messenger of Allah ﷺ was asked, "Which prayer is the best after the obligatory prayers, and which fasting is the best after the month of Ramadan?" He replied, "The best prayer after the obligatory prayers is the prayer in the middle of the night, and the best fasting after the month of Ramadan is the fasting in the month of Muharram."  

سُئِلَ رَسُولُ اللهِ ﷺ أِيُّ الصَّلَاةِ أَفْضَلُ بَعْدَ الْمَكْتُوبَةِ وَأِيُّ الصِّيَامِ أَفْضَلُ بَعْدَ شَهْرِ رَمَضَانَ؟ فَقَالَ أَفْضَلُ الصَّلَاةِ بَعْدَ الْمَكْتُوبَةِ الصَّلَاةُ فِي جَوْفِ اللَّيْلِ وَأَفْضَلُ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ صَوْمُ الْمُحَرَّمِ  

"The Messenger of Allah ﷺ said: 'The best fasting after the month of Ramadan is the month of Allah, Al-Muharram, and the best prayer is prayer at night.'" (Using translation from Nasāʾī 1613)   

كَانَ النَّبِيُّ ﷺ يَقُولُ إِنَّ أَفْضَلَ الصَّلَاةِ بَعْدَ الْمَفْرُوضَةِ الصَّلَاةُ فِي جَوْفِ اللَّيْلِ وَإِنَّ أَفْضَلَ الصِّيَامِ بَعْدَ شَهْرِ رَمَضَانَ شَهْرُ اللهِ الَّذِي تَدْعُونَهُ الْمُحَرَّمَ  

[Machine] That the Messenger of Allah ﷺ used to fast so much that we would say he does not break his fast, and he would break his fast so much that we would say he does not fast.  

أَنَّ رَسُولَ اللهِ ﷺ كَانَ يَصُومُ حَتَّى نَقُولَ لَا يُفْطِرُ وَيُفْطِرُ حَتَّى نَقُولَ لَا يَصُومُ  

The father or Uncle of Mujibah al-Bahiliyyah visited the Messenger of Allah ﷺ. He then went away and came to him (again) after one year when his condition and appearance had changed. He said: Messenger of Allah, do you not recognize me? He asked: Who are you? He replied: I am al-Bahili who came to you last year. He said: What has changed you? You were looking well, then you were good in appearance? He said: I have only food at night since I departed from you. Thereupon the Messenger of Allah ﷺ said: Why did you torment yourself? Fast during Ramadan (the month of patience) and fast for one day every month. He said: Increase it for me, for I have (more) strength. He said: Fast two days. He again said: Increase it for me. He said: Fast three days. He again said: Increase it for me. He said: Fast during the inviolable months and then stop; fast during the inviolable months and then stop; fast during the inviolable months and then stop. He indicated by his three fingers, and joined them and then opened them. (Using translation from Abū Dāʾūd 2428)   

أَنَّهُ أَتَى رَسُولَ اللهِ ﷺ ثُمَّ انْطَلَقَ فَعَادَ إِلَيْهِ بَعْدَ سَنَةٍ وَفِي رِوَايَةِ أَبِي مُوسَى فَأَتَاهُ بَعْدَ سَنَةٍ وَقَدْ تَغَيَّرَتْ حَالُهُ وَهَيْئَتُهُ فَقَالَ يَا رَسُولَ اللهِ أَمَا تَعْرِفُنِي؟ قَالَ وَمَنْ أَنْتَ؟ قَالَ أَنَا الْبَاهِلِيُّ الَّذِي جِئْتُكَ عَامَ أَوَّلَ قَالَ فَمَا غَيَّرَكَ وَقَدْ كُنْتَ حَسَنَ الْهَيْئَةِ قَالَ مَا أَكَلْتُ طَعَامًا مُنْذُ فَارَقْتُكَ إِلَّا بِلَيْلٍ فَقَالَ رَسُولُ اللهِ ﷺ لِمَ عَذَّبْتَ نَفْسَكَ صُمْ شَهْرَ الصَّبْرِ وَمِنْ كُلِّ شَهْرٍ يَوْمًا قَالَ زِدْنِي فَإِنَّ بِي قُوَّةً قَالَ صُمْ مِنْ كُلِّ شَهْرٍ يَوْمَيْنِ قَالَ زِدْنِي فَإِنَّ بِي قُوَّةً قَالَ صُمْ ثَلَاثَةَ أَيَّامٍ زَادَ عَبْدُ الْوَاحِدِ مِنْ كُلِّ شَهْرٍ قَالَ زِدْنِي فَإِنَّ بِي قُوَّةً قَالَ صُمْ مِنَ الْحُرُمِ وَاتْرُكْ يَقُولُهَا ثَلَاثًا وَفِي رِوَايَةِ مُوسَى قَالَ زِدْنِي قَالَ صُمْ مِنَ الْحُرُمِ وَاتْرُكْ صُمْ مِنَ الْحُرُمِ وَاتْرُكْ صُمْ مِنَ الْحُرُمِ وَاتْرُكْ وَقَالَ بِأَصَابِعِهِ الثَّلَاثِ فَضَمَّهَا ثُمَّ أَرْسَلَهَا