Sahih Bukhari Volume 7, Book 71, Hadith Number 626.

Narrated By ‘Abdullah bin ‘Amir : ‘Umar went to Sham and when h ached Sargh, he got the news that an epidemic (of plague) had broken out in Sham. ‘Abdur-Rahman bin ‘Auf told him that Allah’s Apostle said, “If you hear that it (plague) has broken out in a land, do not go to it; but if it breaks out in a land where you are present, do not go out escaping from it.”