Sahih al-Bukhari 278
Bathing (Ghusl)
Whosoever took a bath alone (in seclusion) completely naked
Narrated Abu Huraira: The Prophet (ﷺ) said, 'The (people of) Bani Israel used to take bath naked (all together) looking at each other. The Prophet (ﷺ) Moses used to take a bath alone. They said, 'By Allah! Nothing prevents Moses from taking a bath with us except that he has a scrotal hernia.' So once Moses went out to take a bath and put his clothes over a stone and then that stone ran away with his clothes. Moses followed that stone saying, "My clothes, O stone! My clothes, O stone! till the people of Bani Israel saw him and said, 'By Allah, Moses has got no defect in his body. Moses took his clothes and began to beat the stone." Abu Huraira added, "By Allah! There are still six or seven marks present on the stone from that excessive beating."