Majma al-Zawaid 14310 — The acceptance of Islam by Abu Bakr

Imam al-Sha'bi narrates: I asked Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) who was the first to accept Islam. Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: Have you not heard this verse of Sayyiduna Hassan bin Thabit (may Allah be pleased with him): "When you recall the grief of a trustworthy brother, then also remember your brother Sayyiduna Abu Bakr (may Allah be pleased with him) and his conduct; he is the best of creation, the most God-fearing and the most just, apart from the Prophet (he is the most virtuous), and he fulfilled his responsibilities. He is also the second one, the one who followed, the praiseworthy one, and he is the first person who affirmed the messengers."
Al-Tabarani recorded it. Its chain contains a narrator, al-Haytham bin Adi, and he is matruk (abandoned).