Muwatta Malik #557
Burials
Yahya related to me from Malik from Hisham ibn Urwa that his
father said, "There were two men in Madina, one of whom dug graves
with a niche in the side wall for the body, and the other who did not,
and they said, 'Whichever one comes first can do the job,' and the one
who dug graves with a niche came first and dug the Messenger of
Allah's grave, may Allah bless him and grant him peace."
About Muwatta Malik
This hadith is #557 from Muwatta Malik, in the Book of Burials. Muwatta Malik contains 1,985 hadiths across 61 books.