The World Federation One Stop Fiqh

Ruling 1060

If a person is compelled to perform prayers on muddy ground, in the event that it does not cause him excessive difficulty (mashaqqah) for his body and dress to become soiled with mud, he must perform sajdah and say tashahhud in the normal manner. However, if it does cause him excessive difficulty, he must indicate with his head for sajdah while he is standing and say tashahhud standing as well. In such a situation, his prayer is valid.