Amr bin Mura said, "I heard Zayd bin Arqam say, 'The first to embrace Islam was Ali.'" Amr bin Mura continued, "I mentioned this to Ibrahim al-Nakhai, but he rejected it and said, 'The first to embrace Islam was Abu Bakr al-Siddiq.'"
سمعت زيد بن أرقم يقول: أول من أسلم علي. قال عمرو بن مرة: فذكرت ذلك لإبراهيم النخعي فأنكره. وقال: أول من أسلم أبو بكر الصديق.
Tirmidhi (3735), Ahmad (19281), and Nasai in Al-Kubra (8081) all narrated it through the hadith of Shuba, from Amr bin Mura, from Abu Hamza, who mentioned it, and the wording is Tirmidhi's. Tirmidhi said, "This is a hasan sahih hadith. Abu Hamza's name is Talha bin Yazid."I say, its chain is hasan because of Abu Hamza, for he is hasan al-hadith. See the hadith of the Basin in the Book of Faith.