Is it permissible to donate a large sum of money with the intention of purifying wealth from a suspected unlawful gain, along with the intention of charity for the amount exceeding the unknown suspected portion, and is it permissible to donate money with the intention of purifying it from a suspected unlawful gain preemptively before it occurs?

If one is doubtful about the unlawfulness of their wealth, they should dispose of what they predominantly believe will clear their liability, and the remainder is lawful for them. Al-Qurtubi, in his interpretation of the verse, "O you who have believed, fear Allah and give up what remains [due to you] of interest" (Quran 2:278), stated: "The way to repent from unlawful wealth one possesses, if it is from usury, is to return it to the one from whom usury was taken. If one despairs of finding that person, then they should give it away in charity on their behalf. If it was taken by injustice, they should do likewise. If the matter is unclear to them and they do not know how much is unlawful, then they should estimate the amount in their possession that must be returned until they are certain that what remains is clear for them. They should return it to the one they know they wronged or took usury from. If they despair of finding them, they should give it away in charity on their behalf."

Giving out money with the intention of disposing of future unlawful gains does not clear one's liability, because acts of worship cannot be performed before their cause for obligation arises.