The Conversion of 'Umar bin Al-Khattab took place three days subsequent to the conversion of Hamzah. He was at this time about twenty-six years old, a man of courage who was feared and respected with decisive resolution. Unlike his uncle Abu Jahal he was deeply pious and as such, though a bitter opponent of the new religion, would at times feel various contradictory emotions within his soul. However, the deep-seated bigotry he held rendered him unable to submit to the truth, and thus, persisted in his oppression of Muslims, filled with loathing.

His sharp temper and excessive enmity towards the Prophet led him one day to hunt for the Prophet, and with sword in hand, left his home. However, he didn't get far when he was informed that his brother-in-law and his sister had abandoned polytheism in favour of Islam, and so, 'Umar changed his course setting it towards his sister's house. As he drew near, he could hear the Quran being recited and entered angrily and uninvited. Full of rage he fell upon his brother-in-law beating him severely, but Fatimah his sister rushed to the rescue of her husband when 'Umar fell upon his sister and struck her on her head. Realising fighting back was futile the couple cried out, "Yes, we are Muslims, we believe in God and His Messenger Muhammad so do as you will." Upon seeing the face of his sister besmeared with blood he felt regret, full of shame. He said softly as if to extend an olive branch, "Let me see what you were reading, so that I may see what Muhammad has brought." They complied with his request but only after they had made him wash, since he was unclean. Upon doing so he was given the parchment which he took and began to read, from the opening verses of the Chapter Tâ-Hâ until he reached, "Verily! I am God, none has the right to be worshipped but I, so worship Me and offer prayers for My Remembrance."

'Umar read the verses with awe, and the seed of Islam had finally began to sprout in his heart. "How excellent it is, and how graceful! Please guide me to Muhammad." he said.

Umar then left for Dar Al Arqam where the Prophet had been holding secret meetings along with his Companions. 'Umar reached that place with his sword swinging by his arm. He knocked at the door and the Companions of the Prophet turned to see who the intruder was. One of them peeped through a chink in the door and shrieked, "It's 'Umar with his sword." Hamzah, being the Lion he was, said, "Open the door. If he intends good he shall find it here, and if he intends evil, he will be killed with his own sword." On entering he stated his intentions saying, "O Messenger of God, I come to you in order to believe in God and his Messenger and that which he has brought from his Lord." Filled with delight, all cried out 'God is Great' so loud that even those in the Holy Sanctuary heard.

'Umar's conversion had a tremendous impact on the situation of the believers. Abdullah Ibn Al-'Abbas related that he had asked 'Umar bin Al-Khattab why he had been given the epithet of Al-Faruq (he who distinguishes truth from falsehood), he replied, "After I had embraced Islam, I asked the Prophet: 'Aren't we on the right path in this world and the hereafter?' The Prophet answered: 'Of course you are! I swear by God in Whose Hand my soul is, that you are right in this world and in the hereafter.' I, therefore, asked the Prophet why we then had to conduct clandestine activism. "I swear by God Who has sent you with the Truth, that we will leave our concealment and proclaim our noble cause publicly." We then went out in two groups, Hamzah leading one and I the other. We headed for the Mosque in broad daylight when the polytheists of Quraish saw us, their faces became pale with resentment. On that very occasion, the Prophet attached to me the epithet of Al Faruq."