(38) باب فَضْلِ صَوْمِ الْمُحَرَّمِ
Abu Haraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying:
The most excellent fast after Ramadan is God's month. al-Muharram, and the most excellent prayer after what is prescribed is prayer during the night.
Reference: Sahih Muslim 1163 a
In-book reference: Book 13, Hadith 261
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2611