He, sallallaahu ‘alayhi wa sallam, taught them beneficial supplications:

Under category: How He treated them?

Juwayriyyah (the wife of the Prophet) narrated: The Messenger of Allah, sallallaahu ‘alayhi wa sallam, came out from my room in the morning as I was busy observing my dawn prayer in my place of worship. He, sallallaahu ‘alayhi wa sallam, came back in the forenoon and I was still sitting there. He, sallallaahu ‘alayhi wa sallam, said to me: “Have you been in the same position since I left you?” I said: ‘Yes.’ Thereupon the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: “I recited four words three times after I left you and if these are to be weighed against all what you have recited since morning these would outweigh them and [these words] are: “ Glory be to Allah and praise is due to Him according to the number of His creation and according to the pleasure of His Self and according to the weight of His Throne and according to the ink [used in recording] words [for His Praise]

As-Sindi (a scholar) said: “This means that there are some supplications better than others, because they are more comprehensive and include the names and attributes of Allah. Therefore, shorter and fewer supplications would be more rewarding than others that are more or longer.

The Messenger of Allah, sallallaahu ‘alayhi wa sallam, guided and taught her what to say so that she could get more reward by  exerting a lesser effort.