With regard to how much Hazrat Umar (ra) feared Allah the Almighty, there is a narration in which Hazrat Umar (ra) stated, “Even if a goat perishes on the edge of the Euphrates River, I am fearful that Allah the Almighty will hold me accountable for it on the Day of Judgement.”
(Sirat Umar bin al-Khattab, Ibn al-Juzi, p. 140, al-Matba‘ah al-Misriyyah, al-Azhar)
In another narration, it is mentioned that Hazrat Umar (ra) said, “If a camel perishes on the edge of the Euphrates River, I am fearful that Allah the Almighty will question me about it on the Day of Judgement.”
(Ibn Saad, Al-Tabaqat al-Kubra, Vol. 3 [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 1990], 232.)
Hazrat Anas (ra) bin Malik narrates:
“One day, I was outside with Hazrat Umar (ra) bin al-Khattab when he entered a garden. There was a wall between myself and Hazrat Umar (ra). He was inside the garden. At the time I heard Hazrat Umar (ra) say [to himself], ‘O son of Khattab, bravo! You have become the Leader of the Faithful! By Allah you ought to fear God; otherwise, He will most certainly punish you!’”
(Muwatta Imam Malik, Kitab al-Kalam wa al-Ainah wa al-Tuqa, p. 601, Riwayah number 1867, Maktabah Dar al-Fikr, Beirut)
The following was engraved on Hazrat Umar’s (ra) ring: كَفَى بِالْمَوْتِ وَاعِظًا يَا عُمَرُ
meaning, “O Umar! Death is enough to admonish a person.”
(Ibn ‘Abd al-Barr, Al-Isti‘ab fi Ma‘rifat al-Ashab, Vol. 3, Bab Harf al-Ain, Umar bin al-Khattab [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 2002], p. 236)
That is, if a person always keeps death in mind, then that is enough as an admonishment and enough to reform oneself.
Abdullah bin Shaddad states, “I heard Hazrat Umar (ra) crying profusely while I was standing in the last row [for prayers] He was reciting the following verse:
إِنَّمَآ أَشۡكُوْا بَثِّيْ وَحُزۡنِيْ إِلَى اللّٰهِ
“‘I only complain of my sorrow and my grief to Allah.’ [Ch.12: V.87]”
(Sahih al-Bukhari, Kitab al-Adhan, Bab idha Baka al-Imam fi al-Salah)