Ubayy b. Ka'b said that “Water is necessary only when there is an emission” was a licence granted in the early days of Islam, but that afterwards it was renounced.
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.”
‘Ali reported that a man came to the Prophet and said, “I washed because of sexual defilement, then prayed the dawn prayer but noticed a spot about the size of a nail which had not been touched by the water.” God’s messenger replied, “If you had rubbed your hand over it, it would have been enough for you.”
She also said that the Prophet used to wash his head with marshmallow when sexually defiled, contenting himself with that and not pouring water over it.