Ibn Majah

Commentary:
(1)
This is the characteristic of true certainty: their nature becomes so attuned to the truth and so distant from falsehood that it is no longer possible for them to utter a false statement or commit a wrongful act. In any case, a believer avoids lying. However, this should not be understood to mean that they become infallible (ma‘sum ‘an al-khata’). To be mistaken in some matter due to misunderstanding is one thing, and to deliberately commit a wrongful act is something entirely different. Only the Prophets are infallible (ma‘sum), because they are guided by revelation (wahy); if any action contrary to what is best (khilaf awla) occurs from them, they are immediately alerted, whereas this is not the case for an ordinary member of the community (ummah).

(2)
There are numerous incidents in the life of Umar radi Allahu anhu where, when he expressed an opinion or understanding on a matter, Allah’s command was revealed in accordance with it. The command regarding veiling (hijab), the issue of the prisoners of the Battle of Badr, prayer near the place of Barahim, the matter of the funeral of the chief of the hypocrites, Abdullah bin Ubayy—these are all well-known examples. See: (Sunan al-Kubra lil-Bayhaqi: 88/7). Thus, this correctness of opinion was a special favor and grace from Allah that Umar radi Allahu anhu was granted.

Benefits and Issues:
Despite this greatest praise and commendation, Umar radi Allahu anhu is not infallible from error.
Wherever it was felt that his statement or action was not in accordance with the Qur'an and Sunnah,
the noble Companions radi Allahu anhum ajma'in differed with him.
Unconditional agreement and obedience is due only to Muhammad, the Messenger of Allah sallallahu alayhi wa sallam.