Musnad Ahmad 459:21

Al-Hakam ibn Nafi’ narrated to us, Isma’il ibn ‘Ayyash narrated to us, from Damdam ibn Zur’ah, from Shurayh ibn ‘Ubayd, who said: Al-‘Irbad ibn Sariyah said: The Prophet, peace and blessings of Allah be upon him, would come out to us in the Suffah while we were wearing the *hawtakiyyah* (a type of coarse garment), and he would say: "If you knew what has been stored up for you, you would not grieve over what has been withheld from you. And Persia and Rome shall surely be opened for you."