There is no believing servant who supplicates for his brother behind his back (in his absence) that the Angels do not say: The same be for you too.
Sahih Muslim Book 48, Hadith 119
← Previous Hadith Should I not inform you about the words liked most by Allah? I said: Allah's Messenger, do inform me about the words liked most by Allah. He said: Verily, the words liked most by Allah are:" hallowed be Allah and praise is due to Him."

Sahih Muslim Book 48, Hadith 118 Next Hadith → My husband reported that he heard Allah's Mes- senger (ﷺ) as saying: He who supplicates for his brother behind his back (in his absence), the Angel commissioned (for carrying supplication to his Lord) says: Amen, and it is for you also.

Sahih Muslim Book 48, Hadith 120