Despite Allah Ta’ala blessing Hazrat Umar (radhiyallahu ‘anhu) to be among the ten people that were promised Jannah in this world, and being the second khalifah of Islam, he was extremely humble and greatly feared accountability before Allah Ta‘ala on the Day of Qiyaamah.
It is reported that on one occasion, Hazrat Umar (radhiyallahu ‘anhu) entered a certain orchard while accompanied by Hazrat Anas (radhiyallahu ‘anhu). While in the orchard, he separated from Hazrat Anas (radhiyallahu ‘anhu) and went to another section of the orchard. He was unaware that Hazrat Anas (radhiyallahu ‘anhu) could overhear him, from where he was, and he began to address himself and remind himself of accountability in the Hereafter.
He said, “Umar bin Khattaab! People refer to you by the title, Ameer-ul-Mu’mineen! If you regard this to be excellent, then remember that by Allah, O the son of Khattaab, you will have to certainly fear Allah Ta‘ala in this world, or else He will most definitely punish you!” (Muwatta Imaam Maalik #3638)