Musnad Ahmad 30:1054

And he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The Children of Israel used to bathe naked, looking at one another's private parts. Moses, peace be upon him, used to bathe alone. They said: 'By Allah, nothing prevents Moses from bathing with us except that he has a scrotal hernia.' He said: "So he went one time to bathe and placed his garment upon a stone, and the stone fled with his garment. He said: "So Moses ran after it, saying: 'My garment, O stone! My garment, O stone!' until the Children of Israel looked at the private parts of Moses and said: 'By Allah, there is no defect in Moses.' The stone then stood still until he looked at it, so he took his garment and began striking the stone." Abu Hurairah said: "By Allah, there are six or seven scars on the stone from Moses striking the stone."