What is the ruling on participating in an unlawful abortion, what should have been done, and how is repentance performed?

Assisting in abortion is religiously forbidden. Whoever directly performs the abortion is liable for a blood money (diyya) equivalent to one-tenth of the mother's blood money. Whoever assists in it commits a sin and must perform sincere repentance and show remorse. He or she must also refrain from this reprehensible act.