وروي عن أحدهما عليه السلام قال قلت الرجل يسجد وعليه قلنسوة أو عمامة؟ فقال إذا مس شئ من جبهته الارض فيما بين حاجبيه وقصاص شعره فقد اجزاءه عنه
And it was narrated from one of the two (Imams عليه السلام), peace be upon them, who said: I said: "A man prostrates while wearing a cap or a turban?" He said: “If something from his forehead touches the ground, between his eyebrows and the beginning of his hairline, then it is sufficient for him."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 252