Musannaf Ibn Abi Shaybah

Hazrat Rabi’ bin Khuthaym narrates that Hazrat Abdullah said: Whoever recites these words ten times: There is no deity except Allah, He is alone, He has no partner, His is the dominion and for Him is all praise, and He is powerful over everything — then the reward for these words will be equal to freeing four slaves. The narrator says: I think he said: slaves from the descendants of Ismail.