question #1 Sahih Muslim 920b, Book 11, Hadith 9 : What is the significance of supplicating for the deceased in Islamic tradition?

(O Allah! ) let Thee be the caretaker of what is left by him, and he said: Grant him expansion of the grave, but he did not say: Make his grave spacious. Khalid said: He supplicated for the seventh (thing too) which I have forgotten.