What is the ruling on ẓihār?

Zihar is when a husband likens his wife in unlawfulness to a woman with whom he is محرم (unmarriageable kin). It was considered a divorce in the pre-Islamic era (Jahiliyyah). However, the Lawgiver (Allah) changed its ruling to a temporary prohibition until expiation is performed. It is forbidden and a falsehood. Whoever commits it and then returns (to his wife) must perform the expiation mentioned in the Qur'an.