Musnad Abu Ya'la al-Mawsili 7:14

Muhammad ibn Ishaq al-Musayyibi narrated to us, Abdullah ibn Nafi’ narrated to us, from Hisham ibn Sa’d, from Ibn Shihab, from Abu Salamah ibn Abd al-Rahman, from his father, Abd al-Rahman ibn Awf, that when Umar ibn al-Khattab set out for al-Sham and heard about the plague, he hesitated regarding that. Abd al-Rahman said to him, "I bear witness that I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: 'If you hear of it having occurred in a land, do not enter upon it; and if it occurs while you are in a land, do not exit from it fleeing from it.'" So Umar turned back based on the hadith of Abd al-Rahman ibn Awf.