Actually, mahr is the compensation of the pleasure and delectation a man enjoys from wife. When husband had enjoyed his wife, mahr became wajib on him and he has to pay it. According to Islamic law, paying mahr is wajib on husband. And when husband is prosperous and fully able to pay it, he should pay it. And it is the requisition of the self-respect of husband and it is immodesty to request wife not to take mahr. However, mahr is the right of wife, if she forgives it happily and willingly in the presence of two responsible witnesses in formal way he may be exempted. But in moral pressure only by saying that I do not need mahr, it would not be exempted, she can claim it later.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband