narrated abu huraira (radi-allahu 'anhu):

allah's apostle (sallallahu 'alaihi wa sallam) said, "it is not lawful for a lady to fast (nawafil) without the permission of her husband when he is at home; and she should not allow anyone to enter his house except with his permission; and if she spends of his wealth (on charitable purposes) without being ordered by him, he will get half of the reward."

bukhari vol. 7 : no. 123