Prohibition of facing the Graves during Salat (Prayer)

Imam Al-Nawawi’s Riyad-us-Saliheen
Chapter 342
Prohibition of facing the Graves during Salat (Prayer)

1757. Abu Marthad Kannaz bin Husain (May Allah be pleased with him) said: I heard the Messenger of Allah (sallallaahu ’alayhi wa sallam) saying: “Do not offer Salat (prayer) facing the graves and do not sit on them.”
[Muslim].