What is the ruling on money acquired from selling land that was purchased with money deposited as a trust, after returning the principal amount deposited to its owner?

The money given to you is considered a trust (amanah), and it is not permissible to dispose of it except with the owner's permission. You erred by disposing of it without permission. You must repent to Allah Almighty and guarantee the safekeeping of the trust. As for the money you earned from your disposition of the trust, the most equitable opinion is that it should be divided into two halves: half for you in return for your effort, and half returned to the owner of the money along with the original trust.