It wasnarrated from Safwan bin 'Abdullah bin Safwan said that he wasmarried to a daughter of Abu Darda'. He came to her and found UmmDarda' there, but he did not find Abu Darda'. She said to him:
"Do youintend to perform Hajj this year?" He said: "Yes."She said: "Pray toAllah for us to grant us goodness, for theProphet (ﷺ) used to say:'The supplication of a man for hisbrother in his absence will beanswered. By his head there is anangel who says Amin to hissupplication, and every time he prays forhis brother, he says: "Amin,and the same for you.'" He said:"Then I went out to the marketplacewhere I met Abu Darda', andhe told me something similar from theProphet (ﷺ)."
English reference: Vol. 4, Book 25, Hadith 2895
Arabic reference: Book 25, Hadith 3007