The Messenger of Allah ﷺ said, "There is no Muslim servant who supplicates for his brother in his absence except that the angel says, 'And for you the same.'"In another narration, Umm Darda said, "My master told me that he heard the Messenger of Allah ﷺ say, 'Whoever supplicates for his brother in his absence, the angel appointed over him says, "Amin, and for you the same."'"
قال رسول الله ﷺ: ما من عبد مسلم يدعو لأخيه بظهر الغيب، إلا قال الملك: ولك بمثل. وفي رواية: عن أم الدرداء قالت: حدثني سيدي أنه سمع رسول الله ﷺ يقول: من دعا لأخيه بظهر الغيب قال الملك الموكل به: آمين ولك بمثل.