Sayyiduna Aishah (may Allah be pleased with her) says that the Prophet (peace and blessings be upon him) said: "Whoever of my Ummah leaves a debt and has striven to pay it, but dies before paying it, then I am his guardian (that is, the one who will pay it)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13197