How did Umar (ra) embrace Islam?

In a Nutshell: Umar ibn al-Khattab (ra) heard of his sister's conversion whilst en route to assassinate the Messenger (saw). He saw her with a Qur'anic parchment and angrily slapped her. Her confident stance caused him to read the parchment and he subsequently embraced Islam and met with the the Messenger in Dar al-Arqam. Summary of the Narrations There are a number of narrations describing the conversion of Umar (ra). They differ slightly in marginal aspects of the story but agree on its general outline. Umar (ra) was one of those who used to torture Muslims. One day, he was planning to kill the Messenger (saw) to stop the spread of his message. He took his sword and headed to where the Messenger (saw) used to sit (probably his home). it is improbable he was heading to Dar al-Arqam because after conversion, he asked Muslims to guide him to the Messenger (saw) and they guided him to Dar al-Arqam. One of the companions who hid their faith, probably Nu'aym ibn Abdullah, noticed this intention and asked him where he was heading. Umar (ra) told him he wanted to kill the Messenger (saw). The man diverted his attention by pointing to the Islamic conversion of his own sister Fatimah (ra), advising him to get his own house in order first, as a way of protecting the Messenger (saw). He told him: أَفَلَا تَرْجِعُ إلَى أَهْلِ بَيْتِكَ فَتُقِيمَ أَمْرَهُمْ؟ قَالَ: وَأَيُّ أَهْلِ بَيْتِي؟ قَالَ: خَتَنُكَ وَابْنُ عَمِّكَ سَعِيدُ بْنُ زَيْدِ بْنِ عَمْرٍو، وَأُخْتُكَ فَاطِمَةُ بِنْتُ الْخَطَّابِ، فَقَدْ وَاللَّهِ أَسْلَمَا، وَتَابَعَا مُحَمَّدًا عَلَى دِينِهِ، فَعَلَيْكَ بِهِمَا. "Why aren't you (instead) going to your own household and correcting their matter? Umar replied, 'Who is that in my household?' The man replied, 'Your sister Fatima bint al-Khattab and your cousin Sa'id ibn Zayd ibn Amr embraced Islam and followed the deen of Muhammad. So, you should see them (instead).'" (Ibn Hisham, as-Seera an-Nabawiyyah, Vol. 1, p. 344) Umar went to his sister's house immediately. Inside al-Khabab (ra) was teaching them the Qur'an. Umar knocked on the door and heard the recitation inside. Al-Khabab and another companion hid themselves. On entering, Umar noticing the Qur'anic parchment in her hand questioned them and beat them. However, when he saw the blood on his sister's face and her defiance in the face of his violence, he asked her to give him the parchment. She agreed, provided he undertook ghusl (washing his body) first to purify himself. Umar washed his body and read the Qur'anic words that contained the beginning of sura Taha: طه، مَا أَنزَلْنَا عَلَيْكَ الْقُرْآنَ لِتَشْقَىٰ، إِلَّا تَذْكِرَةً لِّمَن يَخْشَىٰ، تَنزِيلًا مِّمَّنْ خَلَقَ الْأَرْضَ وَالسَّمَاوَاتِ الْعُلَى، الرَّحْمَٰنُ عَلَى الْعَرْشِ اسْتَوَىٰ، لَهُ مَا فِي السَّمَاوَاتِ وَمَا فِي الْأَرْضِ وَمَا بَيْنَهُمَا وَمَا تَحْتَ الثَّرَىٰ، وَإِن تَجْهَرْ بِالْقَوْلِ فَإِنَّهُ يَعْلَمُ السِّرَّ وَأَخْفَى، اللَّهُ لَا إِلَٰهَ إِلَّا هُوَ ۖ لَهُ الْأَسْمَاءُ الْحُسْنَىٰ "Ta, Ha. We have not sent down to you the Qur'an that you be distressed; But only as a reminder for those who fear (Allah) A revelation from He who created the earth and highest heavens, The Most Merciful [who is] above the Throne established. To Him belongs what is in the heavens and what is on the earth and what is between them and what is under the soil. And if you speak aloud - then indeed, He knows the secret and what is [even] more hidden. Allah - there is no deity except Him. To Him belong the best names." (Qur'an 20:1-8) Other narrations state it was sura al-Hadeed (No. 57) such as the narration of Usamah ibn Zayd in Ibn Asakir, Tarikh Dimashq (Vol. 44:33) and al-Bazar, al-Bahr az-Zakhir, (Vol. 1, p. 403). When Umar read these verses, he realized the divine inspiration in them. Al-Khabab (ra) came to him and told him the Messenger (saw) prayed hoping either he or Abu Jahl embraced Islam. Al-Khabab narrated he heard the Messenger (saw) praying: اللَّهُمَّ أَعِزَّ الإِسْلاَمَ بِأَحَبِّ هَذَيْنِ الرَّجُلَيْنِ إِلَيْكَ بِأَبِي جَهْلٍ أَوْ بِعُمَرَ بْنِ الْخَطَّابِ "O Allah! Honour Islam through the dearest of these two men to you: Abu Jahl or Umar ibn al-Khattab." (Tirmidhi 4045) Umar then testified 'There is no God but Allah and Muhammad is His Messenger.' They then guided him to Dar al-Arqam at mount Safa. The Messenger (saw) opened the door. Umar was asked, 'Aren't you going to embrace Islam, O Umar?' Umar embraced Islam and the companions in the house shouted Allahu-Akbar (Allah is the greatest) several times. Objection Some contemporary writers evaluate these historical narrations by stringent juristic conditions for accepting narrations, however whilst this is important and necessary for law, it is usually not required to gain an overview of historic events, so is ignored by most historians. Therefore, they considered these narrations of the conversion of Umar (ra) as da'eef (weak); due to inqitaa (omission of narrators) or narrators lacking a sharp memory along with other conditions. When dealing with historical events, scholars don't give so much attention to the soundness of the narration because the exact terms of the original narration do not matter as there is no hukm (rule) that is being derived, rather more general historic events are being understood. So, scholars instead check the spread of the story or event through different chains of narrators. For differences, scholars evaluate them by comparing all the related narrations and considering what is more likely to have happened. Regarding the narrations of Umar's conversion, it was narrated through many chains of narrators. For example, the following are a number of the story's narrations: Mujahid narrated it on the authority of ibn Abbas (al-Asfahani, Ma'rifat as-Sahabah 3410); Uthman al-Basri narrated it on the authority of Anas ibn Malik (Bayahqi, Dala'il an-Nubuwah, Vol. 2, p. 219-220, Daraqutni, Sunan Daraqutni 441, Ibn Assakir, Tarikh Dimashq, Vol. 44, p. 35); Usamah ibn Zayd ibn Aslam narrated it on the authority of his father who narrated it from his grandfather who heard it from Umar himself (al-Bazar, al-Bahr az-Zakhir, Vol. 1, p. 403, Ibn Asakir, Tarikh Dimashq, Vol. 44, p. 33); Ibn Ishaq narrated it through people whom he did not name (Ibn Ishaq, as-Siyar wa al-Maghazi, pp. 181-184, Ibn Hisham, Vol. 1, pp. 343-346, Ibn Kathir al-Bidayah wa an-Nihayah, Vol. 3. Pp. 100-101); There are other narrations in these cited scholarships on the authority of Aisha, Talha and others. Given this story was narrated through different and dependent chains of narrators, its historical authenticity is quite likely to be accurate. In addition, the narrators of this story are not considered da'eef, such as Usamah ibn Zayd ibn Aslam, because of fabrication or lying, rather their non-sharp memory which is not necessary for historical narratives. We also find many scholars accepted their narrations in a limited context, especially when their narrations are supported by others. (Ibn Uday, al-Kamil fi Du'afa' ar-Rijal, Vol. 2, p. 82) Furthermore, this story was included by almost all the historians, jurists and commentators. See for example, in addition to the above books of seera: Sulili, ar-Rawd al-Aneef, Vol. 3, pp. 161-170; Ibn Abd al-Barr, al-Isti'ab, Vol. 3, pp. 1144-1159; Ibn al-Jawzi, al-Muntadhim fi Tarikh al-Muluk wa al-Umam, Vol. 4, pp. 132-125; Ibn al-Athir, Asad al-Ghabah, Vol. 4, p. 138-144; Ibn Hajar, al-Isabah fi Tameez as-Sahabah, Vol. 4, pp. 484-486; Salihi, Subul al-Huda wa ar-Rashad, Vol. 2, pp. 370-376. This narrative can't be rejected because of the non-sharpness of its reliable and trustworthy narrators. Conclusion Umar (ra) heard of his sister's conversion whilst on route to kill the Messenger. He then embraced Islam and approached the Messenger in Dar al-Arqam and testified the faith.