The World Federation One Stop Fiqh

Ruling 1051

The part of the turbah or the thing on which it is permitted to perform sajdah must be pure. However, if, for example, one places a turbah on an impure carpet, or if one side of the turbah is impure and he places his forehead on its pure side, or if one part of the turbah is pure and another impure, then as long as it does not make the forehead impure, there is no problem.