How to prevent an object from jumping when moving on downslopes?

I'm not a natural to english so excuse me if i miss understud this. But as far as i can read, you want the player can't jump when tu are on a certain angle surface. Is that right? If so, you can check the normal of the contact of collision. I cant remember when and how i did it once. But it have something to be with collisions contacts and contact point normals. I search on the docs but i cant figure how i did it back then. I think i use vector3 angle to check if the normal of the contacted surface si no more than a value, but no sure.