Praise be to Allaah.
Having intercourse with a menstruating woman in her vagina is haraam, because Allaah says-
“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” [al-Baqarah 2:222]
Whoever does that has to seek the forgiveness of Allaah and repent to Him, and he should give a dinar or half a dinar in charity as expiation for what he has done (its nothing but better ie. not compulsory). Ahmad and the authors of al-Sunan narrated with a jayyid isnaad from Ibn ‘Abbaas r. that the Prophet pbuh said: “Whoever has intercourse with his wife when she is menstruating should give a dinar or half a dinar in charity (to poor or needy.)” (which will come according to Bangladeshi taka approximately ৳14500 but if its half of diner then will decrease half of this amount) but after all Whichever you give is sufficient.
Its better to be known that `Diner one kind of gold, which is according to recent calculation equivalent to 4.374grm gold. Which will come in bd taka about 14500...
The most important thing is that. You have to repent to Allaah for going against the prohibition mentioned in this aayah and for not paying heed to the words. That is done by regretting what has happened and resolving not to do it again, and by doing a lot of good deeds, for good deeds wipe out bad deeds. And Allaah is Oft-Forgiving, Most Merciful. ALLAH knows the best
FIQH. DEP. IOM (ISLAMIC ONLINE MADRASA)