Sahih Muslim | Book 5 | Hadith Number 2234

Narrated by 'Aisha
'Aisha reported Allah's Messenger (may peace be upon him) as saying: When a woman spends (something as Sadaqa) out of the household of her husband without causing any damage, there is a reward for her and for him too like it for whatever he earned, and for her (for the wife) because of her spending (for the sake of Allah), and for the trustee also (there is a reward like it), without any reduction from their rewards.