It wasnarrated that Abu Hurairah said:
"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.'" (ID)
English reference (ID): Vol. 1, Book 7, Hadith 1742 (ID)
Arabic reference (ID): Book 7, Hadith 1814 (ID)