Musnad Ahmad 538:4

Hashim narrated to us, he said: Al-Layth narrated to us, from Mu'awiyah ibn Salih, from 'Abd al-Rahman ibn Jubayr, from his father, he said: I heard Abu Tha'labah al-Khushani, a companion of the Messenger of Allah, may Allah bless him and grant him peace, that he heard him saying while he was in al-Fustat during the caliphate of Mu'awiyah—and Mu'awiyah was the one who sent the people to raid Constantinople—he said: "By Allah, this nation will not be incapable of half a day. When you see the Levant as the dining table of one man and his household, then at that time is the conquest of Constantinople."