The Messenger of Allah صلى الله عليه وسلم said, “The supplication of a Muslim for his brother in his absence will certainly be answered. Everytime he makes a supplication for good for his brother, the angel appointed for this particular task says: `Ameen! May it be for you, too’.” [Muslim].
One of the scholars wrote “In this hadith there is a point of benefit to be obtained and that is: if your du’a’ is responded to because your brother is absent from you, then we hope that the angel’s du’a’ for you will also be responded to because you are absent from the angel!”
Thus, I ask you to make du’a’ for the forgiveness of my many sins, [those that are great and those that are small, the first and the last, and those that are apparent and those that are hidden] and know that in return the noble angels will make the same du’a’ for you .