Musannaf Ibn Abi Shayba 27:468

Waki’ narrated to us, from Shu’bah, from ‘Amr ibn Murrah, from Abu Hamzah, the freed slave of the Ansar, from Zayd ibn Arqam, who said: "The first to accept Islam with the Messenger of Allah, may Allah bless him and grant him peace, was ‘Ali." ‘Amr ibn Murrah said: "So I came to Ibrahim and mentioned that to him, and he denied it."