Mishkat al-Masabih 2355

‘Abdallah b. ‘Abbas reported God’s messenger as saying, “A dead man in his grave is just like a drowning man calling for help, for he hopes that a supplication from a father, a mother, a brother, or a friend may reach him, and when it does it is dearer to him than the world and what it contains. God most high brings to those who are in the graves blessings several times as great as the size of the mountains because of the supplication of those who are on the earth. The gift of the living to the dead is to ask pardon for them.” Baihaqi transmitted it in Shu'ab al-iman.