This works (it's obvious the same will hold for negative integers):

    Reduce[a^2 + b^2 == c^2 && 0 < a < 100 && 0 < b < 100 && 0 < c < 100, {a, b, c}, Integers]

![enter image description here][1]


  [1]: https://i.sstatic.net/C9LVv.png