“I would like to thank you for helping me help you.” These words sound strange but this is how sages and wise people think. You see if you help someone, you think you have done a great job but look at it from another point of view.
If there is no one asking help, whom can you help? So that someone who needs and asks for your help is actually doing you a favor asking you! So you should be grateful to that individual who is needy.
In spiritual world, that works in reducing your karmic debt so you should thank the one who asks for help!