It is narrated from Sayyidah Aishah (may Allah be pleased with her) that she said: When Sayyidah Khadijah (may Allah be pleased with her) passed away, Sayyidah Khawlah bint Hakim bin Umayyah bin al-Awqas (may Allah be pleased with her), who was the wife of Uthman bin Maz'un (may Allah be pleased with him), said in Makkah: O Messenger of Allah! Will you not marry? He (peace and blessings be upon him) said: "Whom?" She said: If you wish, a virgin, and if you wish, a previously married woman. He (peace and blessings be upon him) said: "And who is the virgin?" She said: The daughter of the dearest of Allah's creation to you, Aishah bint Abi Bakr. He (peace and blessings be upon him) said: "And who is the previously married woman?" She said: Sawdah bint Zam'ah, who has believed in you and followed you in what you are upon. He (peace and blessings be upon him) said: "Go and mention the two of them on my behalf." So she went and entered the house of Abu Bakr (may Allah be pleased with him) and met Umm Ruman, the mother of Aishah, and said: O Umm Ruman! What good and blessing Allah has brought into your house! The Messenger of Allah (peace and blessings be upon him) has sent me to ask for Aishah's hand on his behalf. She said: I would like you to wait for Abu Bakr; he is about to come. Then Abu Bakr came, and she said: O Abu Bakr! What good and blessing Allah has brought into your house! The Messenger of Allah (peace and blessings be upon him) has sent me to ask for Aishah's hand on his behalf. Abu Bakr said: Is she suitable for him, when she is only his brother's daughter? So he sent me back to the Messenger of Allah (peace and blessings be upon him), and I mentioned this to him (peace and blessings be upon him). He (peace and blessings be upon him) said: "Go back to him and say to him: You are my brother in Islam and I am your brother, and your daughter is suitable for me." So she came back to Abu Bakr, and he said to Khawlah: Call the Messenger of Allah (peace and blessings be upon him) for me. So he (peace and blessings be upon him) came, and he (Abu Bakr) married her to him, and at that time I was six years old.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19363