The World Federation One Stop Fiqh

Ruling 808

The third condition: the clothing that is large enough to cover the private parts on its own of someone performing prayers must not be made from the carcass [of an animal that has not been slaughtered according to Islamic law] and whose blood gushes out when its jugular vein is cut. Based on obligatory precaution, this condition also applies to clothing that cannot cover the private parts on its own. And the recommended precaution is that one should not perform prayers with clothing that has been made from an animal whose blood does not gush out, such as a snake.