It is narrated from Sayyidah Asma' bint Umays (may Allah be pleased with her) that she gave birth to Muhammad bin Abi Bakr at Dhu al-Hulayfah. Abu Bakr (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) ordered him to tell her to take a ritual bath and enter ihram.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20745