Musnad Ahmad 1034:181

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Mansur, who said: I heard Abu Wa'il narrating that Abu Musa used to be strict regarding urine. He said: "The Children of Israel, when urine would touch one of them, he would cut it off with scissors." Hudhayfah said: "I wish he were not so strict. I have seen the Messenger of Allah (peace and blessings of Allah be upon him) come—or he said: walk—to a trash heap of some people, and he urinated while standing."