The ruling on delaying the bathing for Menstruation until the time of Fajr enters
Question :
it permissible to delay the bathing for sexual impurity until the time of Fajr enters, and is it permissible for women to delay the bathing for menstruation or postnatal bleeding until the time of Fajr enters?
Answer:
If the woman sees that she has become pure before the time of Fajr, then she must fast and there is no harm in her delaying the bathing until after the time of Fajr enters. However, she may not delay it until sunrise. Rather, she must bathe and pray before sunrise. Likewise, the sexually impure person may not delay bathing until after sunrise. Rather, he must bathe and pray the Fajr prayer before sunrise. It is also obligatory on the man to make haste in this so that he can catch the Fajr prayer with the congregation.
Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 3 Page 299