What is the difference between ila’ (vow of abstinence from marital relations) and ẓihār (injurious divorce-like pronouncement)? Does the punishment for ẓihār in Surat Al-Mujadilah mean that ila’ is abrogated because it is a form of temporary ẓihār? If not, what is the wisdom behind its permissibility?

Ila' is when a man swears to abstain from intercourse with his wife for more than four months. Allah the Almighty says: {For those who swear to abstain from their wives is a waiting period of four months, but if they return [to her], then indeed, Allah is Forgiving and Merciful.} As for Dhihar, it is when a husband likens his wife or a part of her to a woman who is permanently unlawful for him, such as saying: "You are to me like my mother's back." Allah the Almighty says: {Those among you who declare dhihar from their wives – they are not [actually] their mothers. Their mothers are only those who gave birth to them. And indeed, they are uttering an ill-spoken word and a falsehood.} Dhihar is forbidden and a grave sin, whereas Ila' may be permissible for a legitimate purpose, such as disciplining one's wife, and it has not been abrogated.