It is narrated from Salim that Umar (may Allah be pleased with him) returned with the people based on the hadith of Abdur Rahman bin Awf (may Allah be pleased with him), which he narrated from the Messenger of Allah (ﷺ) regarding not entering a plague-stricken area—that is, when he (Umar) had set out for Syria (from Madinah) and received news of the outbreak of plague there.
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1683
Hadith Takhrijصحیح ثبت موصولا اخرجه البخارى الحيل، باب ما يكره من الاحتيال في الفرار من الطاعون (6973)۔ ومسلم، السلام باب الطاعون والطيرة والكهانة ونحوها (2219)۔