Is it permissible to take a sum of money whose profit was divided equally with a broker who traded with money deposited with him as a trust, knowing that he guarantees the principal in case of loss?

It is not permissible to repay a loan with more than its original amount if this was stipulated or agreed upon. However, if there was no stipulation or agreement, there is no objection to repaying the loan with more or better than its original amount, due to the Hadith of Abu Rafi' in which the Prophet, peace and blessings be upon him, borrowed a young camel (bakr) and returned a superior camel (jamal khayar), saying: "Indeed, the best of people are those who are best in repaying debts."