How can the legal issue be resolved, according to Islamic law, concerning a debt claimed against a father who passed away 20 years ago, where a person claims partnership in the deceased father's trade and demands a sum of money with an unofficial document not recognized by the judiciary, given that the heirs were unaware of this partnership, and the division of the inheritance has been halted due to this dispute?

Whoever claims partnership in a debt must provide lawful proof, for the Prophet, peace and blessings be upon him, said: "If people were given what they claimed, then some people would claim the blood of men and their wealth, but the oath is upon the defendant." The burden of proof is on the claimant, and the oath is on the one who denies. The minimum required to prove financial claims is one man and two women, or one man and the claimant's oath. As for a document written in the father's handwriting, it is not considered lawful proof unless it is established before the judge that it is indeed his handwriting. If the claimant does not provide proof, then he has no claim, and the heirs may distribute the inheritance, unless they acknowledge that the handwriting is that of their deceased relative, in which case they are obligated to give the man what he claimed.