Chapter on the Manner of Prayer, Its Description and What is Obligatory and Recommended

And from him with this same chain of transmission, he said: I asked Abu Abdillah عليه السلام, about a man who prays upon snow. Imam عليه السلام said: "No, but if he is unable to find earth, he should spread his garment and pray upon it." And (Imam عليه السلام was asked) about a man who is caught by rain and is in a place where he cannot prostrate due to the mud and cannot find a dry place. Imam عليه السلام said: "He should begin the prayer, and when he bows, let him bow as usual in prayer, and when he raises his head from bowing, he should gesture for the prostration while standing. He should do that until he completes the prayer, and he should recite the testimony (tashahhud) while standing, then he should conclude with the taslim."