Ja'far bin Muhammad narrates from his father that he said: Jabir (may Allah be pleased with him) narrated to us a hadith, and he was describing the Hajj (Farewell Pilgrimage) of the Prophet ﷺ. He said: When we reached the place of Dhul-Hulaifah, Asma bint Umays (may Allah be pleased with her) gave birth to a child, so the Prophet ﷺ ordered her to perform ghusl (ritual bath) and to enter into ihram.
Hadith Referenceمسند الإمام الشافعي / كتاب الحج / 853
Hadith Takhrijاخرجه مسلم ، الحج، باب صحة احرام النفساء و استحباب اغتسالها للإحرام، وكذا الحائض (1210)۔