Muhammad ibn Ahmad, from Ahmad ibn Al-Hasan, from ‘Amr ibn Sa‘id, from Musaddiq ibn Sadaqah, from ‘Ammar Al-Sabati, from Abu Abdillah عليه السلام, peace be upon him, who said: I asked Imam عليه السلام: “What is the extent of wet mud upon which prostration is not valid?” Imam عليه السلام said: "When the forehead sinks into it and does not remain firmly upon the ground."