The Messenger of Allah ﷺ said, "The best fasting after the month of Ramadan is in Allah's month of Muharram, and the best prayer after the obligatory prayers is the night prayer."
حدثنا قتيبة حدثنا أبو عوانة عن أبي بشر عن حميد بن عبد الرحمن الحميري
قال رسول الله ﷺ أفضل الصيام بعد شهر رمضان شهر الله المحرم وأفضل الصلاة بعد الفريضة صلاة الليل
Muslim also reported it in the Book of Fasting, chapter on the merit of fasting in Muharram, hadith no. 1163, from Qutayba, with the same wording.On this subject there are also narrations from Jabir [Muslim, no. 757], Bilal [to come, no. 3549], and Abu Umama [to come, no. 3549b].