The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness (Kitab Al-Dhikr)

Muslim :: Book 35 : Hadith 6588

Abu Dharr reported that Allah's Messenger (may peace be upon him) said: 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.