(23) باب فَضْلِ الدُّعَاءِ لِلْمُسْلِمِينَ بِظَهْرِ الْغَيْبِ
Abu Dharr reported that Allah's Messenger (ﷺ) 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.
Reference: Sahih Muslim 2732 a
In-book reference: Book 48, Hadith 119
USC-MSA web (English) reference(deprecated numbering scheme): Book 35, Hadith 6588