Praise be to Allaah.
It is haraam (forbidden) for a man to have intercourse with his wife during her period.
Allaah says (interpretation of the meaning):
“They ask you concerning menstruation. Say: that is an Adha (a harmful thing for a husband to have a sexual intercourse with his wife while she is having her menses), therefore, keep away from women during menses and go not unto them till they are purified (from menses and have taken a bath)” [al-Baqarah 2:222].
So it is not permissible for a man to have intercourse with his wife until she has become pure and has taken a bath (made ghusl), because Allaah says (interpretation of the meaning):
“And when they have purified themselves, then go in unto them as Allâh has ordained for you (go in unto them in any manner as long as it is in their vagina).” [al-Baqarah 2:222]
Another indication of how abhorrent this sin is, is the words of the Prophet (peace and blessings of Allaah be upon him): “Whoever has intercourse with a menstruating woman, or has anal intercourse with a woman, or goes to a fortune-teller, has disbelieved in what was revealed to Muhammad.” (Narrated by al-Tirmidhi from Abu Hurayrah, 1/243; see also Saheeh al-Jaami’, 5918).
So you have to prevent him and stop him from doing that. If you obey him in this matter then you will be a partner in the sin with him, but if he forces you to do it then the sin will be on him.please see Question #2121 And Allaah knows best.