It is narrated from Sayyiduna Jabir bin Abdullah (may Allah be pleased with them) that when we reached the place of Baida, Asma bint Umais (may Allah be pleased with her) gave birth to Muhammad bin Abi Bakr. The Messenger of Allah (ﷺ) was informed, so he (ﷺ) said: "Instruct her to perform ghusl (ritual bath), then assume ihram."
Hadith Referenceالسنن المأثورة / باب ما جاء في فدية الأذى / 488
Hadith Takhrijصحیح مسلم، الحج، باب احرام النفساء رقم: 1210۔