Sayyiduna al-Miqdam al-Kindi (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "I am closer to every believer than his own self. Whoever leaves a debt or helpless dependants, it is my responsibility, and whoever leaves wealth, it belongs to his heirs. I am the guardian (wali) of the one who has no guardian: I inherit his wealth and free his captive (that is, pay his blood money and the like). And the maternal uncle is the mawla of the one who has no mawla: he inherits his wealth and frees his captive."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17760