I heard the Messenger of Allah ﷺ say, "The best prayer after the obligatory prayers is the night prayer, and the best fasting after Ramadan is in the month of Allah which you call Muharram."
حدثنا هشام بن عبد الملك الطيالسي حدثنا أبو عوانة عن عبد الملك عن حميد بن عبد الرحمن
سمعت رسول الله ﷺ يقول أفضل صلاة بعد المفروضة صلاة الليل وأفضل الصيام بعد رمضان شهر الله الذي تدعونه المحرم
Its isnad is sahih. Abu Awana is Al-Waddah Al-Yashkuri, and Abdul-Malik is Ibn Umayr. Bukhari related it, 2/214, no. 731, Fath, in the chapter on adhan, night prayer. Muslim related it, 2/821, no. 1163, in the chapter on fasting, the merit of fasting in Muharram. Abu Dawud related it, 2/323, no. 2429. Tirmidhi related it, 2/301, no. 438, and said, hasan sahih. Nasai related it, 2/207, no. 1613.