Musnad Ahmad 25:1286

Muhammad ibn Ja‘far narrated to us, Sa‘id narrated to us, from Qatadah, from Miqsam, from Ibn ‘Abbas: That a man had intercourse with his wife while she was menstruating, so he asked the Messenger of Allah, peace and blessings of Allah be upon him, about that. He ordered him to give a dinar, or half a dinar, in charity.