بسم الله الرحمن الرحيم
Income tax is non-Shariah tax. It is lawful if one can save oneself from it in anyway. Thus the interest of saving bank which you gave in some charitable institution without an intention of reward you can show it in your income tax return. And in this case the amount which you will receive back from income tax department shall be lawful for you. You can use it in any of your needs. However, it should be noted that interest(giving in the possession of poor) money could only be given in such a charitable institution where that amount is spent on poor as a tamlik. You cannot give it to each and every charitable institution.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.