Is it incumbent upon one who has intermingled with his money 1500 Riyals, the unlawfulness of which he suspects, and which resulted from a transaction with a suspicious person, to donate it for the benefit of Muslims to ward off doubts and reassure his heart, regardless of whether he lost or gained in his investment? And does this have any relation to money laundering?

If you suspect that dealing with a suspicious person is unlawful, the 기본 principle is permissibility. However, it is recommended to give away whatever you suspect to be unlawful, dedicating it to charitable projects, as well as the profit share derived from it. This is based on the حديث: "The lawful is clear and the unlawful is clear, and between them are matters that are doubtful." This differs from the ruling on money laundering or profits resulting from unlawful money, which have other rulings.