Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
nasai-kubra:8081 – Ismāʿīl b. Masʿūd > Khālid > Shuʿbah > ʿAmr b. Murrah > Abū Ḥamzah a freed slave of al-Anṣār > Zayd b. Arqam

[Machine] I heard Zaid ibn Arqam saying, "The first person who prayed with the Messenger of Allah ﷺ and said in another place, 'The first person who embraced Islam was Ali.'"  

الكبرى للنسائي:٨٠٨١ – أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ عَنْ خَالِدٍ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ عَمْرِو بْنِ مُرَّةَ قَالَ سَمِعْتُ أَبَا حَمْزَةَ مَوْلَى الْأَنْصَارِ قَالَ

سَمِعْتُ زَيْدَ بْنَ أَرْقَمَ يَقُولُ أَوَّلُ مَنْ صَلَّى مَعَ رَسُولِ اللهِ ﷺ وَقَالَ فِي مَوْضِعٍ آخَرَ أَوَّلُ مَنْ أَسْلَمَ عَلِيٌّ  

See similar narrations below:

Collected by Nasāʾī's Kubrá
nasai-kubra:8336 – Ismāʿīl b. Masʿūd > Khālid / Ibn al-Ḥārith > Shuʿbah > ʿAmr b. Murrah > Abū Ḥamzah a freed slave of al-Anṣār > Zayd b. Arqam

[Machine] I heard Zaid bin Arqam saying, "The first person to pray with the Messenger of Allah ﷺ was Ali." And he said in another place, "Ali was the first to convert to Islam."  

الكبرى للنسائي:٨٣٣٦ – أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ عَنْ خَالِدٍ وَهُوَ ابْنُ الْحَارِثِ قَالَ حَدَّثَنَا شُعْبَةُ عَنْ عَمْرِو بْنِ مُرَّةَ قَالَ سَمِعْتُ أَبَا حَمْزَةَ مَوْلَى الْأَنْصَارِ قَالَ

سَمِعْتُ زَيْدَ بْنَ أَرْقَمَ يَقُولُ «أَوَّلُ مَنْ صَلَّى مَعَ رَسُولِ اللهِ ﷺ عَلِيٌّ» وَقَالَ فِي مَوْضِعٍ آخَرَ «أَسْلَمَ عَلِيٌّ»