We are talking today (9)reported directly from the Prophet, may Allah’s pea

Umm Ad-Dardaa’, may Allah be pleased with her, reported directly from the Prophet, may Allah’s peace and blessings be upon him, that he said, “The supplication of a Muslim for a fellow Muslim in his absence is answered. At his head, there is an entrusted angel. Whenever one invokes good for his brother, the entrusted angel says, 'Ameen, and likewise to you.'”

Explanation

Allah accepts the invocation that a Muslim makes for his brother, who is absent and does not know about it. So when he supplicates, an angel stands at his head and says, “Ameen,” that may you have the same good that you have invoked for your brother.