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.
Lalle ne Allah Yanã umurnin ku ku bãyar da amãnõni zuwa ga mãsu sũ. Kuma idan kun yi hukunci a tsakãnin mutãne, ku yi hukunci da ãdalci. Lalle ne Allah mãdalla da abin da Yake yi muku wa'azi da shi. Lalle ne Allah Yã kasance Mai ji ne, Mai gani.
Yã kũ waɗanda suka yi ĩmãni! Kada ku yaudari Allah da ManzonSa, kuma ku yaudari amãnõninku, alhãli kuwa kunã sane.
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.