Is a wife's request for an amount exceeding what she loaned her husband considered usury?

If a loan stipulates repayment with an increase, then it is forbidden usury (riba). Usury is one of the gravest sins, and there is no difference in this regard whether it is between spouses or others.

However, if no increase is stipulated, and the husband voluntarily gives an increase upon repayment, then there is no harm in that, for the Prophet, peace and blessings be upon him, said: "Indeed, the best among people are those who are best in paying off their debts."