Is the son obligated to repay his deceased father's debt, in light of a dispute over the nature of the amount the son previously paid to his father—was it a loan or a partnership in purchasing land—given the absence of documents or witnesses?

The questioner is advised first to reconcile and resolve the dispute amicably, due to the discord between brothers causing strife. The bonds of kinship must be preserved, and the Companions, may Allah be pleased with them, were an example in ceding rights for the sake of brotherhood.

Regarding the jurisprudential issue: if the owner of the money claims that the money was a qirad (profit-sharing partnership), and the recipient claims it was a loan, the jurists have differed on this matter, with several opinions: Some jurists held that the statement of the owner of the money is to be accepted. Some jurists held that the statement of the recipient (borrower) is to be accepted. Some jurists held that the statement of the one claiming it was a loan should be given precedence, because it is more burdensome for the recipient and because his hand is on the money and the profit. If each party presents evidence, the more probable view is to give precedence to the recipient's evidence because it contains additional knowledge.

Since the matter is subject to scholarly disagreement, reconciliation is preferable. Otherwise, the matter must be referred to the Sharia court.