It is narrated from Sayyiduna Buraydah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "O Buraydah! Soon armies will be dispatched, so join the army of Khurasan, then go to the city of Marw, for no harm will befall its inhabitants, because Dhu al-Qarnayn built it."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1140