A man visited Maran Harav Chayim Kanyevsky Shlit"a, and was discussing various personal things.
Amongst the issues brought up was that he and his wife are suffering from mice running around their house. Maran asked him if he gives Maaser Kesofim. He said that his financial situation was quite difficult and that he found it hard to give maaser. Maran told him that if he gives Maaser he will not have this problem. The man started giving and the mice disappeared.