Yes. The Quran commands returning trusts to their owners (4:58) and forbids betraying them (8:27). This includes money left with you, secrets, and the duties of a job. Delaying payment of a debt when you are able to pay is also a form of injustice.
Sesungguhnya Allah menyuruh kamu menyampaikan amanat kepada yang berhak menerimanya, dan (menyuruh kamu) apabila menetapkan hukum di antara manusia supaya kamu menetapkan dengan adil. Sesungguhnya Allah memberi pengajaran yang sebaik-baiknya kepadamu. Sesungguhnya Allah adalah Maha Mendengar lagi Maha Melihat.
Hai orang-orang yang beriman, janganlah kamu mengkhianati Allah dan Rasul (Muhammad) dan (juga) janganlah kamu mengkhianati amanat-amanat yang dipercayakan kepadamu, sedang kamu mengetahui.
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Questions about halal and haram
Is it haram to betray a trust?
Yes. The Quran commands returning trusts to their owners (4:58) and forbids betraying them (8:27). This includes money left with you, secrets, and the duties of a job. Delaying payment of a debt when you are able to pay is also a form of injustice.
