question #3 Sahih Muslim 956, Book 11, Hadith 93 : What is the impact of the Prophet’s prayer on the graves of the deceased according to this narration?

Lead me to her (or his) grave. They led him to that place and he said prayer over her (or him) and then remarked: Verily, these graves are full of darkness for their dwellers. Verily, the Mighty and Glorious Allah illuminates them for their occupants by reason of my prayer over them.