Question:
Is there any proof that the mark that develops on the
forehead from prostration is a sign of righteousness?
Answer:
This is not a sign of righteousness; rather, light on
one’s face, calmness in ones chest, good manners,
and the like are. As for the mark that results from
prostrating, it even shows up on the face on those
people who only pray the obligatory prayers, from
some kind of sensitivity in their skin. And it does not
appear on the faces of some people who pray often
and who prolong their prostrations.
Shaykh Muhammad bin Saalih al-`Uthaymeen