Amir al-Sha'bi (may Allah have mercy on him) narrated: I asked Sayyiduna Ibn Abbas (may Allah be pleased with them both): Who was the first person to accept Islam? He said: Abu Bakr. Have you not heard these verses of Hassan bin Thabit (may Allah be pleased with him):
"When you recall the grief of a trustworthy brother, then remember your brother Abu Bakr for what he did."
"The best of creation, the most God-fearing and the most just of them, except the Prophet (peace and blessings be upon him), and the most faithful in fulfilling what he bore."
"And the second, the one who followed (the Prophet, peace and blessings be upon him), whose presence is praiseworthy, and the first of the people to affirm the truth of the messengers."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12509