What is the ruling on a prize from a Qur'anic competition that was entered despite violating the condition of "not participating in a similar competition"?

Observing the condition imposed by one Muslim upon another, in matters that are permissible, is obligatory. This is based on the saying of the Prophet, peace and blessings be upon him: "Muslims are bound by their conditions." Therefore, this prize is not lawful for you, and giving charity or donating it does not absolve you of it, as long as it is possible to return it to its rightful owners. You must seek absolution from whoever has the right to dispose of it, or return it to the concerned party.