ما الدليل على تحريم مس النجاسة دون مقتضى؟

Those who argue against deliberately soiling oneself with impurities—outside of prayer and without necessity—cite the hadith: "Cleanse yourselves from urine, for indeed, most of the torment of the grave is due to it." This hadith conveys a command to avoid urine and purify oneself from it, because failing to cleanse oneself from it is a cause for punishment in the grave. This includes both one's own urine and that of others, and from it, the prohibition of deliberately soiling oneself with urine without necessity is inferred.