What is the Sharia ruling on a man who assaulted his wife's sister and raped her by force? And what is the advice for someone who does not want his sister to be exposed?

Adultery is one of the major sins and is forbidden in all religions due to the diseases, killings, hatred, and crimes it causes. It mixes lineages, destroys chastity, and brings Allah's wrath and punishment. Allah has warned against it by saying: "And do not approach unlawful sexual intercourse. Indeed, it is ever an indecency and an evil way." (17:32). The ugliness of adultery increases if it is rape. What this man did is a heinous crime, but concealing a Muslim's faults is praiseworthy in Islamic law, as the Prophet, peace and blessings be upon him, said: "Whoever conceals a Muslim's fault, Allah will conceal his fault on the Day of Resurrection." Therefore, it is advisable to conceal the matter and warn this person. Your friend should beware of seeking revenge against him through killing or other means, as Allah Almighty says: "But whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment." (4:93). And the Prophet, peace and blessings be upon him, said: "A believer remains within the scope of his religion as long as he does not shed forbidden blood."