Urwah bin al-Zubayr (may Allah have mercy on him) reported that Sayyidah Aishah (may Allah be pleased with her) said: "Ever since I came of understanding, I found my parents only upon Islam, and not a single day passed except that the Messenger of Allah (peace and blessings be upon him) came to our house morning and evening."
Imam Ahmad (may Allah have mercy on him) said: Sayyidah Aishah (may Allah be pleased with her) was born upon Islam, because her parents were upon Islam from the very beginning. It is also narrated from Sayyidah Aishah (may Allah be pleased with her) that when the Messenger of Allah (peace and blessings be upon him) married her she was six years old, when she was sent to his house she was nine, and when he (peace and blessings be upon him) passed away she (may Allah be pleased with her) was eighteen years old. Sayyidah Asma' bint Abi Bakr (may Allah be pleased with her), however, was born in the Jahiliyyah, and then became Muslim through her father's Islam, because when she emigrated to the Prophet (peace and blessings be upon him) she was pregnant with Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both). Sayyidah Asma' (may Allah be pleased with her) gave birth to him (Ibn al-Zubayr) in Quba', and she did not nurse him until she brought him to the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) rubbed something on his palate (did tahnik) and supplicated for him, and he was the first child born in Islam after the arrival in Madinah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12146