What are the foundational sources for establishing legal rulings concerning trusts (Amanat)?

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The foundations for legal rulings are the Book (Quran), the Sunnah (Prophetic Tradition), and scholarly consensus (Ijma). Evidence from the Quran includes the injunctions to render trusts to their rightful owners (Quran 4:58) and the command to fulfill trusts if one is entrusted by another (Quran 2:283). The supporting Sunnah is the Prophet's saying: 'Render the trust to the one who entrusted it to you, and do not betray the one who betrayed you.' It is also narrated that the Prophet left deposits with Umm Ayman upon Hijra and instructed Ali to return them to their owners. Consensus among scholars of every era affirms the permissibility of entrusting goods (Iida') and being entrusted with them (Isteeida'), necessitated by public need as not everyone can safeguard their own wealth.