The Prophet ﷺ proposed to Abu Bakr for the hand of Ayesha.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 لخطبة 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 Book of Marriage (5081) from Abdullah bin Yusuf, who said, Layth told us, from Yazid, from Iraak, from Urwa, who mentioned it. Its form is mursal, as a group of scholars have said, including Ismaili, Daraqutni, Abu Naeem, Abu Masud, and others. But it appears on the surface that he took this from his aunt Ayesha, or from his mother Asma bint Abu Bakr. That is why Ibn Abdul-Barr said, "When it is known that the narrator met the one he reported from, and he was not a mudallis, this is taken to mean that he heard it from the one he reported from, even if he did not use a wording that indicates that." See Fath al-Bari (9/124).