What is the ruling on assuming liability for a debt that is already due or stating, 'What I have given is upon me'?

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If one assumes liability for a debt after it has become obligatory, or declares, 'What I have given is upon me,' then that which is confirmed as given becomes binding upon the assumptor. Guarantee (Daman) means joining the liability of the guarantor to the liability of the principal debtor concerning the obligation of the right. Thus, the right becomes binding upon both of them, and the right-holder may pursue either one. The permissibility of guarantee is established by the Quran, Sunnah, and consensus. The evidence from the Quran is the verse: {And whoever produces it [a load of grain], there will be for him a burden [of grain] and I am responsible for it} [Quran 12:72], where Ibn Abbas interpreted 'za'im' as the guarantor. The evidence from the Sunnah includes the Prophet's statement: "The guarantor is liable" (reported by Abu Dawud and Al-Tirmidhi, who graded it Hasan). Furthermore, the Prophet Muhammad (peace be upon him) refused to pray the funeral prayer for a man until Abu Qatada guaranteed his two dirhams debt, whereupon the Prophet prayed for him.