Ibn ‘Abbas reported the Prophet (May peace be upon him) as saying; when a man has intercourse with his wife while she is menstruating, he must give half a dinar in alms. Abu Dawud said; ‘Ali b. Budhaimah reported similarly on the authority of Miqsam from the Prophet (May peace be upon him). Al-Awza’I narrated from Yazid b. Abi Malik, from ‘Abd al-Hamid b. ‘Abd al-Rahman from the Prophet (May peace be upon him); He ordered him to give two fifth of a dinar in alms. But this is a chain where two narrators (Miqsam and Ibn ‘Abbas) are missing. (Using translation from Abū Dāʾūd 266)
"إِذَا وقَعَ الرَّجلُ بأهْلهِ وَهِيَ حائِضٌ فليتصَدَّقْ بنصفِ دينارٍ".