قَالَ قَالَ أَبُو بَكْرٍ أَلَسْتُ أَحَقَّ النَّاسِ بِهَا أَلَسْتُ أَوَّلَ مَنْ أَسْلَمَ
“ِAm I not the most deserving of it among the people, Am I not the first to become Muslim…”
Source: Al-Tirmidhee, Sunan, vol. 6, kitaab manaaqib, ch. abu bakr’s merits, pg. 351, hadeeth # 3667 (hadeeth # 4029 in some versions)
Al-Albaani graded this hadeeth SaHeeH in SaHeeH wa Da`eef Sunan Al-Tirmidhee, vol. 8, pg. 167, hadeeth # 3667
Aboo Taahir Zubayr `Alee Al-Za’i said this hadeeth is SaHeeH in Sunan Al-Tirmidhee, vol. 6, pg. 351, hadeeth # 3667
أَلَسْتُ أَوَّلَ مَنْ أَسْلَمَ أَلَسْتُ صَاحِبَ كَذَا
Sayyidina Abu Sa’eed Khudri (RA) reported that Abu Bakr (RA) said, “Am I not the most deserving of all people. Am I not the first of those who embraced Islam. Am I not the companion of so-and-so? Am I not the companion of so-and-so?”
Source: Al-Tirmidhee, Sunan, book on merits, chapter 37-No caption, 3687
Jalaludin Suyuti (Sunni Scholar) in his book Tarikh ul-Khulafa (History of the Caliphs), he died in 911 A.H.
Here some reports on what has been stated on who was the first to become a Muslim (Typed up below)
Abu Sa’id al-Khudri said: Abu Bakr said, “Am I not the most suitable of the people for it (the khilafah)? Am I not the first to accept Islam? Am I not the one of such and such? Am I not the one of such and such?”
Al-Harith related that “Ali, said the first among the men to accept Islam was Abu Bakr”
Zaid bin Arqam said: The first to perform the prayer with the Prophet, was Abu-Bakr as-Siddiq.
Abu Arwa ad-Dawsi the Companion, said: “The first to accept Islam was Abu Bakr as-Siddiq.”
Furat ibn as-Sa’ib said: (long part I cut out)… There is a disagreement as to him and Khadijah (which of them was first to accept Islam) until (it is said that) he married her to him, and all of that before the birth of Ali.
A whole group of the Companions and the Followers said that he was the first to accept Islam, and some of them claimed that there was a consensus on that. It has been said, “The first to accept Islam was “Ali”. It has also been said, “Khadijah”. The reconciliation between these apparently conflicting statements is that Abu Bakr was the first man to accept Islam, “Ali was the first of the children to accept, and Khadijah was the first woman to accept Islam.
Salim ibn Abi’l-Ja’d said: I said to Muhamamd ibn al-Hanafiyyah, “Was Abu Bakr the first person to accept Islam? He said, “No”. I said, “So how did Abu Bakr excel and precede others so much so that no-one else is mentioned but ABu Bakr?” He said, “Because he was the best of them in Islam from the moment he accept Islam until the moment he met his Lord.”
Muhammad ibn Sa’d ibn Abi Waqqas said to his father Sa’d, “Was ABu Bakr the first of you to accept Islam?” He said, “No. More than five people accepted Islam before him, but he was the best of us in Islam.”
Ibn Kathir said: It is clear that the people of his house, believed before anyone, his wife Khadija, his freed slave Zaid, Zaid’s wife Umm Ayman, “Ali and Waraqah.”
Source: Jalaludin Suyuti, Tarikh ul-Khulafa (History of the Caliphs) pg. 18-19.