Narrated by Sayyiduna Abu Huraira (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: When the husband is present, his wife should not observe a voluntary fast without his permission, and in the presence of the husband, she should not allow anyone to enter the house without his permission. And whatever a woman spends from her husband's earnings without his order, she will receive half the reward for it.
Benefits: … What is meant here is a voluntary (nafl) fast, but if one considers the purpose and objective of the ruling, then the same ruling will apply to making up obligatory (fard) fasts as well. That is, regarding the make-up (qada) of Ramadan fasts, a woman should also consult her husband.
By "this expenditure" is meant those things which are generally given as charity, for example, five or ten rupees, a handful of flour or wheat, bread, curry, etc. A valuable item cannot be spent without the husband's permission. Furthermore, the value of an item will be determined according to the household circumstances, and if the husband explicitly forbids even giving away a trivial thing as charity, then the wife will have no authority in this matter.
A voluntary (nafl) fast is a great act of worship and carries immense reward, but the husband's right has been given precedence over it.