Musnad Ahmad 1682

It was narrated from "Abdullah bin ‘Amir bin Rabee"ah that "Umar bin al-Khattab set out towards Syria. When he was in Sargh, he heard that an epidemic had broken out in Syria. ‘AbdurRahman bin "awf told him that the Messenger of Allah (ﷺ) said. “If you hear of it in some land, do not go there; if it occurs in some land and you are there, do not leave it, fleeing from it.” So ‘Umar bin al-Khattab returned from Sargh.