Mūsa (peace be upon him) was a bashful man who used to cover his skin completely out of extreme bashfulness. So some of the children of Israel abused him

Prophet Mūsa (Moses)(peace be upon him) was a man of abundant bashfulness. He always loved to cover himself so that his skin would not be seen out of bashfulness. The Children of Israel verbally abused him. They said that he covered himself as such because he had a skin defect like leprosy or scrotal hernia (i.e. a bulging groin), or some other defect or disease. So, Allah wanted to prove to them that Mūsa was not suffering any of that.

One day, he was alone, so he put his clothes on a stone and bathed. After the bath, he went to take his clothes but the stone ran with the clothes on it. Mūsa took his staff and ran naked after the stone, asking it to give him his clothes back. While running, he passed by a group of the Children of Israel who saw him naked and saw that he had perfect skin. They knew then that he had no skin defects. Mūsa caught up with the stone and took his clothes and put them on.

He then hit the stone with his staff, leaving on it three, four, or five marks. Allah, the Exalted, referred to this incident in the Qur'an, in the following verse: {O you who have believed, be not like those who abused Moses; then Allah cleared him of what they said. And he, in the sight of Allah, was distinguished} [Sūrat al-Ahzāb: 69].

It warns the believers not to abuse Prophet Muhammad (may Allah's peace and blessings be upon him) as the Children of Israel abused Mūsa, who had an honorable status with Allah, the Almighty, and so Allah cleared him of what they had falsely attributed to him.