Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.102.

It is permissible for the wife to give sadaqah from her husband’s holdings if she knows that he would not mind. However, it is unlawful if she is not sure of this: It is related from ‘Aishah that the Messenger of Allah, upon whom be peace, said: “When a wife gives something as sadaqah from the food of her home without causing any waste, she will get the reward for what she has given. Her husband will be rewarded for what he has earned, and the keeper (if any) will be similarly rewarded. The one does not reduce the reward of the other in any way.” This is related by al-Bukhari.

Abu Umamah reports that he had heard the Messenger of Allah, upon whom be peace, saying in a sermon during the year of the Farewell Pilgrimage: “The wife should not spend anything from the household of her husband without his permission.” He asked: “O Messenger of Allah, upon whom be peace! Not food either?” He said: “That is the most excellent of our holdings.” This is related by at-Tirmizhi who graded it hassan.

Of small things which she is in the habit of giving, no permission from her husband is called for: It is related from Asma, daughter of Abu Bakr, that she said to the Messenger of Allah, upon whom be peace: “Zubair is a well-off man. A man in need approached me and I gave him sadaqah from my husband’s household without his permission.” The Messenger of Allah, upon whom be peace, said: “Give what you are in the habit of giving of what is small, and do not store property away, for Allah shall withhold his blessings from you.” This is related by Ahmad, al-Bukhari, and Muslim.