Musnad Ahmad 30:2093

Nuh narrated to us, Abdullah—meaning al-Umari—informed us, from Khubayb ibn Abd al-Rahman, from Hafs ibn Asim, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "It is imminent that people will return to Medina, until their outposts become at al-Silah."