“A man came to the Prophet (ﷺ) and said: ‘Which fasting is better after the month of Ramadan?’ He said: ‘The month of Allah which is called Muharram.’”
Sunan Ibn Majah Book 7, Hadith 105
← Previous Hadith “I came to the Prophet (ﷺ) and said: ‘O Prophet of Allah, I am the man who came to you last year.’ He said: ‘Why do I see your body so thin (and weak)?’ He said: ‘O Messenger of Allah! I do not eat during the day; I only eat at night.’ He said: ‘Who commanded you to punish yourself?’ I said: ‘O Messenger of Allah! I am strong enough.’ He said: ‘Fast the month of patience* and one day after it.’ I said: ‘I am strong enough (to do more).’ He said: ‘Fast the month of patience and two days after it.’ I said: ‘I am strong enough (to do more).’ He said: ‘Fast the month of patience and three days after it, and fast the sacred months.’”

Sunan Ibn Majah Book 7, Hadith 104 Next Hadith → The Prophet (ﷺ) forbade fasting Rajab.

Sunan Ibn Majah Book 7, Hadith 106