It is narrated from Sayyidah Asma' bint Umays (may Allah be pleased with her) that she gave birth to Muhammad bin Abi Bakr at al-Bayda'. Abu Bakr (may Allah be pleased with him) mentioned this to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Tell her to take a ritual bath (ghusl) and then enter ihram."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20737