Bukhari

Hadith Commentary:
This applies when the woman knows of the husband's consent.
If the woman is not trustworthy, then she must never be permitted to spend in this manner.
In the verse: ﴿فَالصَّالِحَاتُ قَانِتَاتٌ حَافِظَاتٌ لِلْغَيْبِ﴾ (),
it is evident from "by what Allah has preserved" that this is the meaning intended for this ummah.

Hadith Commentary:
(1)
This applies in the case when the woman knows of the husband's consent. Furthermore, if the woman is not trustworthy, then she should not be permitted to spend; such charity and almsgiving are not obligatory. Despite this, the wife is allowed to spend, but what is incumbent upon the husband and is his obligation, she is even more entitled to take from that.
(2)
The woman receives half the reward for giving charity because she herself is a participant in the food present in the house; therefore, she is deemed deserving of half the reward.
(‘Umdat al-Qari: 14/371, 372)

Hadith Commentary: The meaning is that a woman should give such a small charity that even if her husband sees it, he would not dislike it—for example, giving some food from a meal to a poor person, or giving an old, worn-out garment in the way of Allah. And the woman understands from circumstantial evidence that her husband permits such charity, even though he has not given explicit permission. Some have said that what is meant is that the woman spends from the wealth which the husband has allocated for her.

In some versions, it is stated that the husband will receive half the reward of the woman.

Qastallani said that one of these two explanations must be adopted; otherwise, if a woman spends her husband's wealth without his permission, then instead of reward, sin would be incurred.

Hadith Commentary:
(1)
The meaning of "ghayr muqsidah" (غير مقسدة) is that the wife should not spend her husband's wealth in unlawful places and expenditures.

(2)
Here, a question arises: if the food belongs to the husband, then the wife cannot spend it, and if it belongs to the wife, then the husband has no say in it.
The answer to this is given as follows: the food is indeed the husband's, but the custom is that husbands grant their wives permission to spend from the household food upon the poor and needy. Furthermore, another question may arise: when a woman spends without her husband's explicit permission, how can she be rewarded for it? The answer to this is that sometimes the husband has granted general permission to spend, but at the specific moment he does not give a direct order to do so; in such a case, she will receive half the reward because, although permission exists, the explicit command is absent.
In any case, spending the husband's wealth without his permission carries the risk of sin rather than reward, provided that the husband considers it objectionable.

1687. Commentary:
➊ The arrangement and management of household finances, so that the balance between income and expenditure is maintained, is among the husband's obligations. Therefore, it is necessary to obtain permission before giving charity (sadaqah) beyond what is customary and habitual. If, after giving charity, the husband is pleased, then the wife receives half the reward.
➋ By "customary and habitual" is meant sending ordinary cooked food to neighbors, giving to a beggar, or certain occasional matters.

Benefit:
In this hadith, there is a very important message for women: whenever she wishes to observe a voluntary fast (nafl), she should first seek permission from her husband. If permission is granted, then she may fast; otherwise, she should not fast. From this, it is understood that a woman should always be ready to obey her husband. He may call his wife for intimacy at any time of the day or night, so it should not happen that the husband calls his wife and she presents the excuse of fasting, saying, "I am observing a voluntary fast." It is prohibited for a wife to observe a voluntary fast without her husband's permission.