I heard the Messenger of Allah ﷺ say, "After me there will be many military expeditions. Be among the expedition to Khurasan, then settle in the city of Marw, for Dhul-Qarnayn built it and prayed for it to be blessed, and no harm shall befall its people."
حدثنا الحسن بن يحيى من أهل مرو حدثنا أوس بن عبد الله بن بريدة قال أخبرني أخي سهل بن عبد الله بن بريدة عن أبيه
سمعت رسول الله ﷺ يقول ستكون بعدي بعوث كثيرة فكونوا في بعث خراسان ثم انزلوا مدينة مرو فإنه بناها ذو القرنين ودعا لها بالبركة ولا يضر أهلها سوء
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Its chain of transmission is daif, because of Aws bin Abdullah bin Burayda and his brother Sahl bin Abdullah, both of whom are agreed to be daif. Haythami said the same in 10/64, but he only weakened Aws and said nothing about Sahl. It is found in Tabarani's Al-Kabir, 2/19, number 1151. He included it in Ilal Mutanahiya among the unreliable reports, 1/309, number 494, but mentioned in Al-Qawl Al-Musaddad that it has a corroborating narration. This will be discussed further ahead.