Musannaf Ibn Abi Shayba 33:640

Waki' narrated to us, from Mis'ar, from Ibrahim, from Muhammad ibn al-Muntashir, from Masruq, who said: "There is nothing better for the believer than a *lahd* (a niche in the side of a grave), for he has found rest from the worries of the world and has become secure from the punishment of Allah."