Ahmad ibn Muhammad from Mu'ammar ibn Khallad, who said:
I asked Abu Al-Hasan عليه السلام, about prostrating upon snow. Imam عليه السلام said: "Do not prostrate in the salt marsh nor upon snow."
Ali Akbar al-Ghaffari
Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 2, p. 334