Jami` at-Tirmidhi 3735
جامع الترمذي#3735SahihNarrated a man from the Ansar:that Zaid bin Al-Arqam said: "The first to accept Islam was 'Ali." 'Amr bin Murrah said: "So I mentioned that to Ibrahim An-Nakha'i, so he rejected that and said: 'The first to accept Islam was Abu Bakr As-Siddiq
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih Isnaad
Al-AlbaniSahih Isnaad
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 49:132