Searching for title..Please help!

It was the early to mid 80,s I saw the film and was the best kung fu movie I have ever seen. Any help would be greatly appreciated. It was about I pretty sure 3 Kung fu fighters who were defeated by a master so they all learned special techniques to fight him again. the only technique I remember was one kept forcing his hands into sand to make them strong enough to kill the master. there were great fight scenes. any help with this would be great!.

thank you,
Rock