Those who are doing ‘Dhihar’ from among you to their wives—they do not become their mothers; indeed, their mothers are none except those who gave them birth; indeed, they are saying words prohibited and falsehood; and Allah is the Pardoning, the Forgiving.
The word ‘Dhihar’ means pointing out, comparing, exemplifying, etc. In the ignorant period, there existed a custom of ‘Dhihar’. That is, a husband, by saying to his wife, "You are to me just like my mother," kept/abstained his wife from having sex without divorcing her. Through this verse, Allah gives a verdict that it is prohibited as well as falsehood. But due to ignorance, if it happens from anyone, then after getting Knowledge, if he seeks forgiveness from Allah for it, Allah will pardon it and forgive it for him. See explanation 4: 17-18; 25: 68-70; and 33: 4.