When a woman is menstruating, I read that before she goes to sleep she has to check if her menses has ended. Is this only when going to sleep at night or anytime for example, during the night she might be woken up by a noise, does she leave her bed to check? Or she might nap during the day, does she check?
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
A woman must check whether or not she is pure (from her menses) if she doubts that she might have become pure, lest she misses the prayer. She needs to check at the time of every prayer and before going to bed at night.
However, it is not obligatory for her to do so at times other than the prayer times, like if she wanted to have a nap during the day. She is also not obliged to do that if she wakes up during the night. If she knew that she had not become pure by night, then this would be sufficient and she can wait until she wakes up for the Fajr prayer and check at that time.
For more benefit, please refer to Fataawa 51702 and 355546.
Allah knows best.