What evidence is required for a person claiming to be indebted when requesting Zakat funds designated for debtors?

Primary text

If a person claims to owe a debt, and the claim is made for the purpose of reconciling disputes (islāh dhāt al-bayn), the matter is usually clear, but if hidden, acceptance requires authenticated proof (bayyinah). If the debt was incurred for the benefit of the claimant himself (ghurim li-maslahati nafsihi), proof is also required, as the default legal position is non-indebtedness and discharge of liability. If the creditor confirms the debt, there are two related legal considerations, similar to the ruling concerning a maktūb (a slave purchasing his freedom) whose master confirms his status.