Bukhari

Hadith Commentary:
These slaves were Bilal, Zayd ibn Harithah, Amir ibn Fuhayrah, Abu Fukayhah, and Ubayd ibn Zayd al-Habashi. Among the women were Khadijah and Umm Ayman, or Sumayyah. In summary, among the free men, the very first to embrace faith was Abu Bakr as-Siddiq (radi Allahu anhu), among the children was Ali (radi Allahu anhu), and among the women was Khadijah (radi Allahu anha).

Hadith Commentary:
➊
The five slaves were:
Hazrat Bilal bin Abi Rabah, Hazrat Zayd bin Harithah (radi Allahu anhu), Hazrat Amir bin Fuhayrah (radi Allahu anhu), Abu Fukayhah (radi Allahu anhu), and Ubayd bin Zayd al-Habashi (radi Allahu anhu). And among the women were Hazrat Khadijah al-Kubra (radi Allahu anha) and Hazrat Umm Ayman (radi Allahu anha) or Hazrat Sumayyah (radi Allahu anha).
➋
The position of Hazrat Ammar (radi Allahu anhu) is that Hazrat Abu Bakr (radi Allahu anhu) was the first among the free people to openly declare his Islam. Otherwise, there were countless Muslims who kept their Islam concealed. Among the children, Hazrat Ali (radi Allahu anhu) was the first to accept Islam, and among the women, Hazrat Khadijah (radi Allahu anha) was the first to accept Islam.
➌
Imam Bukhari (rahimahullah) has established from this hadith the precedence of Hazrat Abu Bakr (radi Allahu anhu) in Islam.
And Allah knows best.

Hadith Commentary:
Abu Bakr as-Siddiq radi Allahu anhu was born in Makkah two years before the incident of the People of the Elephant, and he passed away in Jumada al-Akhirah, 13 AH, at the age of 63 years.
The duration of his caliphate was two years and four months.
His five slaves were: Bilal, Zayd, Amir, Abu Fakiha, and Ubayd; and the two women were Khadijah and Umm Ayman or Sumayyah radi Allahu anhunna.
Abu Bakr was called "as-Siddiq" because even in the time of ignorance (Jahiliyyah), he never lied nor engaged in idol worship.
Qadi Abu al-Husayn narrated with his chain that Abu Bakr’s father, Abu Quhafah, once took him to the idol house and said to him, "Prostrate to the idol."
He said this and left.
Abu Bakr relates: I went to one of the idols and said to it, "I am hungry, give me food."
It gave no reply.
Then I said, "I am naked, clothe me."
Still, the idol gave no reply.
Finally, I picked up a stone and said, "If you are a god, then protect yourself from me."
Saying this, I struck the idol with the stone and then fell asleep there.
Meanwhile, my father came and said, "Son, what are you doing?" I replied, "What you see."
He took me to my mother and told her the whole story.
She said, "Do not say anything to my son. Allah, the Exalted, spoke to me because of him when he was in my womb. When I began to feel pain, I heard a voice say, 'O bondwoman of Allah, rejoice! You will be given a free boy whose name in the heavens is as-Siddiq. He will be the companion and friend of Muhammad sallallahu alayhi wa sallam.'"

Hadith Commentary:
➊
The first five slaves to embrace faith at the hand of the Messenger of Allah (sallallahu alayhi wa sallam) are:
Bilal (radi Allahu anhu), Zayd (radi Allahu anhu), Amir (radi Allahu anhu), Abu Fakiha (radi Allahu anhu), and Ubayd (radi Allahu anhu).
And two women: Khadijah (radi Allahu anha) and Umm Ayman (radi Allahu anha) or Sumayyah (radi Allahu anha).

➋
This hadith indicates that Abu Bakr (radi Allahu anhu) was the first to become Muslim, because Ammar (radi Allahu anhu) narrates that among men, only Abu Bakr (radi Allahu anhu) was with the Messenger of Allah (sallallahu alayhi wa sallam), and it was he who purchased Bilal (radi Allahu anhu) and set him free so that he might be saved from the torment inflicted by the polytheists due to his acceptance of Islam.
(Fath al-Bari: 7/214)