The Prophet ﷺ approached Abu Bakr to ask for Ayesha's hand in marriage.Abu Bakr said to him, "But I am your brother."He replied, "You are my brother in the religion of Allah and His Book, and she is lawful for me to marry."
أن النبي ﷺ يخاطب عائشة إلى أبي بكر، فقال له أبو بكر: إنما أنا أخوك، فقال: أنت أخي في دين الله، وكتابه، وهي لي حلال.
Bukhari narrated it in the chapter on marriage (5081), from Abdullah bin Yusuf, who said, Layth narrated to us, from Yazid, from Irak, from Urwa, and he related it. Its form is mursal, as a group of scholars have said, including Ismaili, Daraqutni, Abu Naeem, Abu Masud, and others. However, its apparent sense is that he received this either from his aunt Ayesha or from his mother Asma bint Abu Bakr. That is why Ibn Abdul-Barr said, "When it is known that a narrator met the person from whom he is reporting, and he is not known to practice tadlis, this is taken to mean that he heard it from the one he is reporting from, even if he does not use a wording that explicitly indicates this." See Fath al-Bari (9/124).This is supported by what Tabarani narrated in Al-Kabir (23/23-24), from Muhammad bin Abdus bin Kamil Sarraj, who said, Saeed bin Yahya bin Saeed Umawi narrated to us, who said, my father narrated to me, from Muhammad bin Amr, from Yahya bin Abdul-Rahman bin Hatib, from Ayesha, who said, "When Khadijah died, Khawla bint Hakeem bin Umaya bin Awqas, the wife of Uthman bin Mazun, said, while this was in Makkah, 'Messenger of Allah, shall I not find you a wife?' He said, 'Who?' She said, 'If you wish, a virgin, and if you wish, a previously married woman.' He said, 'Who is the virgin?' She said, 'The daughter of the person most beloved to you among Allah's creation, Ayesha bint Abu Bakr.' He said, 'And who is the previously married woman?' She said, 'Sawda bint Zama, who has believed in you and followed you in what you stand for.' He said, 'Then go and mention them both to me.'She came and entered the house of Abu Bakr, and found Umm Ruman, the mother of Ayesha, and said, 'Umm Ruman, what good and blessing has Allah brought into your household? The Messenger of Allah ﷺ has sent me to propose to Ayesha.' She said, 'I wish you would wait for Abu Bakr, for he is coming.' Abu Bakr then came, and she said, 'Abu Bakr, what good and blessing has Allah brought into your household? The Messenger of Allah ﷺ has sent me to propose Ayesha to him.' He said, 'Is she suitable for him? She is only his brother's daughter.' So he sent me back to the Messenger of Allah ﷺ, and I mentioned that to him, and he said, 'Go back to him and tell him, you are my brother in Islam and I am your brother, and your daughter is suitable for me.'So she went to Abu Bakr, and he said to Khawla, 'Call the Messenger of Allah ﷺ for me.' He came, and he married him to her, and I was at that time six years old."Its chain of transmission is hasan because of Muhammad bin Amr bin Alqama, for he is hasan al-hadith. Haythami said in Al-Majmu (9/225), "Tabarani narrated it, and its men are the men of the Sahih, apart from Muhammad bin Amr bin Alqama, and he is hasan al-hadith."