question #1 Sahih al-Bukhari 1336, Book 23, Hadith 91 : What is the significance of praying at a grave according to Islamic teachings?

I heard Ash-Shu`bi saying, “I was told by a man who had passed with the Prophet (p.b.u.h) by a grave
that was separate from the other graves that he (the Prophet (ﷺ) ) led them in the prayer and they prayed
behind him.” I said, “O Abu `Amr! Who narrated that to you?” He replied, “Ibn `Abbas.”