The Canons of the Council in Trullo; Often Called The Quinisext Council 18Canon XVIII.

Those clerics who in consequence of a barbaric incursion or on account of any other circumstance have gone abroad, we order to return again to their churches after the cause has passed away, or when the incursion of the barbarians is at an end. Nor are they to leave them for long without cause. If anyone shall not have returned according to the direction of this present canon--let him be cut off until he shall return to his own church. And the same shall be the punishment of the bishop who received him.