The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, said: "It is not permissible for a man to pray while wearing a turban (‘imamah) or a veil (litham) such that his forehead is covered; he must uncover the spot of prostration on his forehead and uncover his mouth for recitation of the Qur'an.” As for uncovering the forehead, we have already explained earlier that it is necessary, and it is further clarified by what was narrated:
Commentary #37