Abdullah bin Abbas reported,

Abbas, Ali, and Fadl entered the grave of the Messenger of Allah ﷺ, and a man from the Ansar dug the niche in the side of the grave. He was the same man who used to dig the niches for the graves of the martyrs.

Azami 3806

Sahih

عن عبد الله بن عباس قال

دخل قبر رسول الله ﷺ العباس وعلي والفضل، وشق لحده رجل من الأنصار، وهو الذي يشق لحود قبور الشهداء.

الأعظمي 3806صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Funerals
Chapter
Graves
Section
Niche grave and placing bricks over the deceased
Numbering
Jami al-Kamil 3806 (2nd edition)
Azami 3806