Abd al-Jabbar bin Wa'il (may Allah have mercy on him) narrates from his father that he said: I prayed with the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) heard a man saying: "Allahu akbaru kabira, wa subhanallahi wa bihamdihi kathira (Allah is the Greatest, greatly; and glory and praise be to Allah, abundantly)." When he (peace and blessings be upon him) finished the prayer, he said: "Who said that phrase?" He said: I intended nothing by it but good. He (peace and blessings be upon him) said: "The gates of the heaven were opened for it, and nothing held it back short of the Throne."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18277