Hawzah News Agency – The merciful prophet of Islam (pbuh) says:

إنّ المَعصيَةَ إذا عَمِلَ بها العَبدُ سِرّاً لم تَضُرَّ إلّا عامِلَها، وإذا عَمِلَ بها عَلانِيَةً ولم يُغَيَّرْ علَيهِ أضَرَّت بالعامَّةِ.

'If a servant [of Allah] was to secretly sin, he would only harm himself, and if he was to commit it openly and he is not stopped, people would be harmed by it.'

Source: Bihar al-Anwar, v. 100, p. 74, no. 15