The purity of the heart is a condition for the validity of prostration to God Almighty, based on the fact that it is prostrating, and the purity of the limbs at the time of prostration is reasonable from the meaning, because at the time of prostration they are not acting in any matter other than the heart. Therefore, if the servant’s heart prostrates, it will never be raised while the limbs are in a state. Prostrating outside of prayer is an act of worship that does not require the use of water or dirt in its performance, and if it is in purity, it is better and better. Abdullah bin Omar, may God be pleased with him, used to prostrate for recitation without purity.