What should I do if I see a man committing adultery with my brother's wife: should I go to court without witnesses, or tell my brother what I saw, or remain silent?

Adultery is a major sin, and accusing someone of it without fulfilling the conditions for its proof is among the destructive sins. Allah Almighty says: "And those who accuse chaste women and then do not produce four witnesses - lash them with eighty lashes and never accept from them a testimony, and those are the defiantly disobedient" (Quran 24:4). And Allah Almighty says: "Why did they not produce for it four witnesses? And when they have not produced the witnesses, then it is they, in the sight of Allah, who are the liars" (Quran 24:13). The conditions for witnesses to adultery are seven: that they be four, men, free, just, Muslims, that they describe the adultery precisely, and that they come forward in one sitting. Informing the court without these conditions being met is considered slander that necessitates punishment. What is obligatory is to prevent indecency through admonition and reminding of Allah, to conceal their sin if they repent, and to inform the brother if they persist.