Mishkat al-Masabih 447

Ya'la told of God's messenger seeing a man washing in a public place, so he mounted the pulpit, and when he had praised and extolled God he said, “God is characterised by modesty and concealment and loves modesty and concealment, so when any of you washes he should conceal himself.” Abu Dawud and Nasa’i transmitted it, but in Nasa’i's version he said, “God is characterised by concealment, so when any of you intends to wash, he should hide behind something.”