Musa ('alayhi sallam) said, “My Lord, teach me something with which I can remember You and call upon You.”

Allah said, “Say: there is no God but Allah ( لاَ إِلَهَ إِلاَّ اللَّهُ ).”

Musa said ('alayhi sallam), “My Lord, all Your servants say this.”

Allah said, “O Musa, if the seven Heavens along with their inhabitants besides Me and the seven Earths were to be upon a scale, and the statement that there is no God but Allah ( لاَ إِلَهَ إِلاَّ اللَّهُ ), they would be outweighed by the saying: there is no God but Allah ( لاَ إِلَهَ إِلاَّ اللَّهُ ).”

 
[Sahih Ibn Hibban, Number 6218, Sahih]