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.
Воистину, Аллах велит вам возвращать вверенное на хранение имущество его владельцам и судить по справедливости, когда вы судите среди людей. Как прекрасно то, чем увещевает вас Аллах! Воистину, Аллах - Слышащий, Видящий.
О те, которые уверовали! Не предавайте Аллаха и Посланника и не покушайтесь на то, что вверено вам, сознательно.
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.