It is narrated from Qasim (may Allah have mercy on him) that Sayyida Asma bint Umais (may Allah be pleased with her) gave birth to Muhammad bin Sayyiduna Abu Bakr (may Allah be pleased with him) at the place of Bayda. So Abu Bakr Siddiq (may Allah be pleased with him) mentioned this to the Messenger of Allah (ﷺ), so he (ﷺ) said: "Instruct her to perform ghusl (ritual bath), then enter into ihram."
Hadith Referenceالسنن المأثورة / باب ما جاء في فدية الأذى / 487
Hadith Takhrijسنن نسائی، الحج، باب الغسل للاهلال، رقم: 2663، وقال الالبانی صحیح، مسند احمد: 22/45، رقم: 27084 وقال الارنوؤط : حديث صحيح۔