Musnad Ahmad 788:84

Bahz narrated to us, Shu'bah narrated to us, Abu al-Tayyah narrated to us, from a sheikh of theirs, from Abu Musa, who said: The Messenger of Allah (peace and blessings of Allah be upon him) leaned toward soft ground beside a wall and urinated. Shu'bah said: I said to Abu al-Tayyah, "While sitting?" He replied, "I do not know." He said: Then the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the Children of Israel, when urine touched them, they would cut it away with scissors. So, if one of you urinates, let him seek a place for his urine."