Is it permissible for a wife to waive her maintenance (nafaqa) for her poor husband while she is well-off?

The basic principle is that the maintenance of the wife and children is obligatory upon the husband. There is no blame upon the wife for waiving her right to maintenance; this act is considered a kindness and an act of worship for which she will be rewarded. The Prophet, peace and blessings be upon him, said to Zaynab, the wife of Ibn Mas'ud: "Ibn Mas'ud spoke the truth; your husband and your children are more deserving of the charity you give to them."