Mishkat al-Masabih 135

Jabir said: We went out with God’s messenger to [the funeral of] Sa’d b. Mu’adh when he died. God’s messenger prayed over him, and when he was placed in his grave and the ground was levelled over him, God’s messenger extolled God and we did so also at great length. He then said, “God is most great,” and we did the same. Someone asked him why he had extolled God and then said, “God is most great,” to which he replied, “This upright servant’s grave had closed in on him, but finally God removed the pressure from him.”
Ahmad transmitted it.