(23) باب الصَّلاَةِ عَلَى الْقَبْرِ
Anas reported that the Messenger of Allah (ﷺ) observed prayer on the grave.
Reference: Sahih Muslim 955
In-book reference: Book 11, Hadith 92
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 2087