´It was narrated from Asma bin 'Umais that:` she gave birth to Muhammad bin Abi Bakr As-Siddiq in Al-Baida, Abu Bakr told the Messenger of Allah about that, and he said: "Tell her to perform Gusl then begin the Talbiyah.''
Explanation & Benefits
Hafiz Muhammad Ameen
(1) Asma bint Umais radi Allahu anha was the honorable wife of Abu Bakr radi Allahu anhu. This incident took place during the journey of Hajjat al-Wada'. Before entering into ihram, Muhammad ibn Abi Bakr was born in this very valley.
(2) The command for ritual bath (ghusl) given to Asma radi Allahu anha was not for purification (taharah), because this was the period of postnatal bleeding (nifas), but rather this ghusl was for ihram. It is thus understood that performing ghusl for ihram is a Sunnah; otherwise, the Messenger of Allah sallallahu alayhi wa sallam would not have instructed a woman in nifas to perform ghusl. However, it is not obligatory. In place of ghusl, ablution (wudu) is also sufficient, but ghusl is superior.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 2664