Bukhari

Hadith Commentary:
(1)
When Abdur Rahman ibn Awf radi Allahu anhu narrated to them the hadith of the Messenger of Allah sallallahu alayhi wa sallam, they firmly resolved to return. In the narration of Musannaf Ibn Abi Shaybah, it is mentioned that Umar radi Allahu anhu felt regret upon returning and used to supplicate as follows:
“O Allah! Forgive my returning from Sargh.”
(al-Musannaf li-Ibn Abi Shaybah: 7/28, no. 33837)
His expression of regret was because he had set out for a very significant expedition, and when he reached near the intended destination, he turned back. Had he waited at a nearby place for the plague to end, he could have then proceeded on his expedition. The plague ended soon thereafter.

(2)
Perhaps, when he received news that it ended quickly, he expressed regret over it, because the hardship and mental distress endured in returning would not have been experienced had he waited. Moreover, the hadith was a prohibition against going there, not about returning from there.
(Fath al-Bari: 10/230)
And Allah knows best.

Takhrij al-Hadith: [الموطأ رواية يحييٰ بن يحييٰ 896/2، 897 ح 1722، كه 45، ب 7، ح 24، التمهيد 210/6، الاستذكار : 1654، أخرجه البخاري 5730، 6973، و مسلم 2219، من حديث مالك به]
Jurisprudential Points:
➊ It is narrated from Salim bin Abdullah bin Umar rahimahullah that Sayyiduna Umar radi Allahu anhu turned back due to the hadith of Abdur Rahman bin Awf radi Allahu anhu. [صحيح بخاري: 6973 و صحيح مسلم: 2219/100]
This is a lofty example of following the Sunnah.
➋ A solitary report (khabar wahid) is authoritative, provided that the narrator is trustworthy and truthful.
➌ If a person in a plague-stricken area becomes afflicted by the plague, it is quite possible that his creed may become corrupted. This is likely the reason why it has been prohibited to enter or leave a plague-affected area.
➍ The love of the noble Companions radi Allahu anhum for the Prophet sallallahu alayhi wa sallam is unparalleled.

Hadith Commentary: Benefits and Issues: From the statement of Hazrat Salim radi Allahu anhu, it is understood that the firmness in Hazrat Umar’s radi Allahu anhu resolve was produced only after hearing the hadith. From some narrations, it is known that Hazrat Umar radi Allahu anhu expressed regret upon his return, so it is possible that when the epidemic ended quickly, he may have thought that if he had stayed in Sargh and then gone to Shaam after the epidemic had ended, the purpose for which he had set out on the journey would also have been fulfilled, and he would have acted upon the hadith as well. It is not the case that his opinion had changed and that he had come to consider entering an epidemic-stricken area as permissible.