Sahih Bukhari | Volume 7 | Hadith Number 123

Narrated by Abu Huraira
Allah's Apostle 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."