Chapter 20: The Book of Qiyam Al-Lail (The Night Prayer) and Voluntary Prayers During the Day
It was narrated from Abu Bishr Ja' far bin Abi Wahshiyyah that: He heard Humaid bin 'Abdur-Rahman say: "The Messenger of Allah (ﷺ) said: 'The best prayer after the obligatory (fard) prayers is prayer at night and the best fasting after the month of Ramadan is Al-Muharram.'" Shu' bah bin Al-Hajjaj narrated it in Mursal form.
Sunan an-Nasa'i 1614