I arrived in Sham and went to Abu Darda's home, but I did not find him there. Instead, I found Umm Darda, who asked me, "Do you intend to make the pilgrimage this year?"I said, "Yes."She said, "Then pray to Allah for good on our behalf, for the Prophet ﷺ used to say, 'The supplication of a Muslim for his brother in his absence is answered. At his head is an angel appointed to his task, and whenever he prays for his brother with good, the appointed angel says, "Amin, and may you have the like."'"He said, So I went out to the market and met Abu Darda, who said the same thing to me, narrating it from the Prophet ﷺ.
قدمت الشام فأتيت أبا الدرداء في منزله فلم أجده ووجدت أم الدرداء، فقالت: أتريد الحج العام؟ فقلت: نعم قالت: فادع الله لنا بخير فإن النبي ﷺ كان يقول: دعوة المرء المسلم لأخيه بظهر الغيب مستجابة، عند رأسه ملك موكل كلما دعا لأخيه بخير، قال الملك الموكل به: آمين، ولك بمثل. قال: فخرجت إلى السوق فلقيت أبا الدرداء فقال لي مثل ذلك يرويه عن النبي ﷺ.
Muslim narrated it in "Remembrance and Supplication" (2733) from Ishaq bin Ibrahim, from Isa bin Yunus, who said, Abdul-Malik bin Abu Sulayman narrated to us, from Abu Zubayr, from Safwan, and he related it.The most well known version narrated on this subject is from Umar bin Khattab, who said, "I asked the Prophet ﷺ for permission to perform Umrah, and he gave me permission and said, 'Do not forget us, my brother, in your supplication.'" In another version, "O my brother, include us in your supplication and do not forget us." Abu Dawud narrated it (1498) with the first wording, and Tirmidhi (3562) and Ibn Majah (2894) with the second wording, all of them from the hadith of Asim bin Ubaydullah, from Salim, from Ibn Umar, from Umar, and he related it.Imam Ahmad narrated it (195) through this same route and said, and he later said in Madinah, "O my brother, include us in your supplication." Umar then said, "I would not trade it for whatever the sun rises upon," because of his saying "O my brother." His statement "and he later said in Madinah" refers to Shuba, as Abu Dawud made explicit. Its chain is daif because of Asim bin Ubaydullah, that is, Asim bin Ubaydullah bin Asim bin Umar bin Khattab, the Madinan, who is considered daif by the majority of scholars.However, he was not the only one to narrate it, for Khatib narrated it in his "Tarikh" (11/396) through another route, from Asbat bin Muhammad, from Sufyan Thawri, from Ubaydullah, from Nafi, from Ibn Umar, and he related it. But he quoted from Barqani, who said, "No one has corroborated Abu Ubayd on this, rather the correct version is what he narrated from Zafarani, from Shababa, from Shuba, from Asim bin Ubaydullah, from Salim, from Ibn Umar, from Umar." Khatib responded to this, saying, "Others besides Abu Ubayd have narrated it from Zafarani, agreeing with Abu Ubayd's version." He went on at length about this.The conclusion is that this hadith is not reliably preserved as coming from Asbat bin Muhammad, from Sufyan Thawri, from Ubaydullah. Rather, it is the hadith of Thawri and others from Asim bin Ubaydullah. For Asbat bin Muhammad, although he is trustworthy, Ibn Main, Ibn Saad, and others considered him reliable, was nonetheless judged weak with regard to his narrations from Thawri, due to his frequent disagreement with Thawri's well known companions, among them Waki, Muammal bin Ismail, and Qasim Jarmi, and others.