It is narrated from Sayyidah Asma' bint Umays (may Allah be pleased with her) that she gave birth to a child at Dhu al-Hulayfah, and the Prophet (peace and blessings be upon him) ordered her to take a ritual bath and enter ihram.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20739