(23) باب فَضْلِ الدُّعَاءِ لِلْمُسْلِمِينَ بِظَهْرِ الْغَيْبِ
Safwan (and he was Ibn 'Abdullah b. Safwan, and he had been married to Umm Darda') reported:
I visited Abu Darda's house in Syria. I did not find him there but Umm Darda' (was present at the house). She said: Do you intend to perform Hajj during this year? I said: Yes. She said: Do supplicate Allah for blessings upon us, for Allah's Apostle (may peace be upon hiin) used to say: The supplication of a Muslim for his brother at his back (in his absence) is responded so long as he makes a supplica- tion for blessings for his brother and the commissioned Angel says: Amen, and says: May it be for you too I I went to the bazar and met Abfi Dardi' and he narrated like this from Allah's Messenger (ﷺ).
Reference: Sahih Muslim 2733, 2732 c
In-book reference: Book 48, Hadith 121
USC-MSA web (English) reference(deprecated numbering scheme): Book 35, Hadith 6590