"A man asked Ali: "Which month do you order me to fast after the month of Ramadan?' He said to him, 'I have not heard anyone ask this except for a man whom I heard asking the Messenger of Allah while I was sitting with him. He said: "O Messenger of Allah! Which month do you order me to fast after the month of Ramadan?" He said: "If you will fast after the month of Ramadan, then fast Al-Muharram, for indeed it is Allah's month in which there is a day that Allah accepted the repentance of a people, and in which He accepts the repentance of other people."  

عَنْ هَذَا إِلاَّ رَجُلاً سَمِعْتُهُ يَسْأَلُ رَسُولَ اللَّهِ ﷺ وَأَنَا قَاعِدٌ فَقَالَ يَا رَسُولَ اللَّهِ أَىُّ شَهْرٍ تَأْمُرُنِي أَنْ أَصُومَ بَعْدَ شَهْرِ رَمَضَانَ قَالَ إِنْ كُنْتَ صَائِمًا بَعْدَ شَهْرِ رَمَضَانَ فَصُمِ الْمُحَرَّمَ فَإِنَّهُ شَهْرُ اللَّهِ فِيهِ يَوْمٌ تَابَ اللَّهُ فِيهِ عَلَى قَوْمٍ وَيَتُوبُ فِيهِ عَلَى قَوْمٍ آخَرِينَ  

A man came to the Prophet ﷺ and said O Messenger of Allah, tell me of a month that I can fast after Ramadan. The Messenger of Allah ﷺ said: “If you want to fast a month after Ramadan, then fast al-Muharram, for it is the month of Allah and in it is a day on which Allah forgave people and will forgive more people.ʿ  

أَتَى النَّبِيَّ ﷺ رَجُلٌ فَقَالَ يَا رَسُولَ اللهِ أَخْبِرْنِي بِشَهْرٍ أَصُومُهُ بَعْدَ رَمَضَانَ فَقَالَ رَسُولُ اللهِ ﷺ إِنْ كُنْتَ صَائِمًا شَهْرًا بَعْدَ رَمَضَانَ فَصُمِ الْمُحَرَّمَ فَإِنَّهُ شَهْرُ اللهِ وَفِيهِ يَوْمٌ تَابَ فِيهِ عَلَى قَوْمٍ وَيُتَابُ فِيهِ عَلَى آخَرِينَ  

" عَنْ عَلِىٍّ قَالَ: سَأَلَ رَجُلٌ رَسُولَ الله ﷺ وَأَنَا قَاعِدٌ فَقَالَ: يَا رسُولَ الله أى شَهْرٍ تَأمرنى أنْ أصومَ بَعْدَ شَهْرِ رَمَضَانَ؟ قَالَ: إِنْ كُنْتَ صَائِمًا بَعْدَ شَهْرِ رَمَضَانَ فَصُم المُحَرَّمَ فَإِنَّهُ شَهْرُ الله، وَفِيهِ يَوْمٌ تَابَ الله فِيهِ عَلَى قَوْمٍ وَيَتُوبُ فِيهِ عَلَى آخَرِينَ".