Hadithcore
Musnad Ahmad 2032
sahih

It was narrated from Ibn 'Abbas, from the Prophet (ﷺ) about one who has intercourse with his wife when she is menstruating:

“Let him give a dinar or half a dinar in charity.” 'Abdullah said: My father said: And neither ‘AbdurRahman nor Bahz attributed it to the Prophet (ﷺ) .

References1 variant
Arabic/English book
Book 25, Hadith 2032