What is the expiation for a man who asked his Christian wife to abort their fetus, which was 41 days old, and he now feels guilty and wants forgiveness?

Aborting a fetus is forbidden at all stages, unless its continued presence poses a danger to the mother's life. The blood money (diyah) for it is obligatory, according to the more preponderant opinion, and it is safer to also perform expiation (kaffarah). The diyah and kaffarah are obligatory upon the one who directly performed the abortion, not on the one who ordered it or assisted in it. If you did not directly perform the abortion, then only repentance is required of you.