Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.137B.
Section : Menstruating or post-childbirth bleeding women.
If the blood of a menstruating woman or of a woman with post-childbirth bleeding stops during the night, she can delay ghusl until the morning and still fast but, she must perform ghusl before the morning prayer.