2,141. A Heretical Practice
Hilchos Issurei Biah 11:15
Similar to the previous halacha, in some places the practice is for a woman who has given birth to a boy to refrain from marital intimacy until 40 days have passed and for a woman who has given birth to a girl to refrain until 80 days have passed even if they only saw blood on the seven days immediately following delivery. While this practice can be found in the writings of some Geonim, it is nevertheless incorrect. The responsa in which this practice can be found are mistaken and the practice itself is heretical because it is learned from the Sadducees. It is a mitzvah to get people to uproot this practice and return to the words of the Sages who only require counting seven clean days as has been explained.
Hilchos Issurei Biah 11:16
A woman doesn’t leave the condition of ritual impurity and stop being considered a forbidden relationship until she immerses in a valid mikvah with nothing in between her skin and the water. In Hilchos Mikvaos, we will discuss IY”H what renders a mikvah valid or invalid, how to immerse and the laws of interpositions. If a woman who needs to immerse only washes in a bath, she remains ritually unclean and sexual relations with her would render one liable to the penalty of kareis (spiritual excision). This would be the case even if all the water in the world passed over her. The only way to leave the condition of ritual impurity is to immerse in a mikvah, a spring, or a sea that’s like a spring. Again, this will all be covered IY”H in Hilchos Mikvaos.