They then told the king that the prince had claimed that were he in charge of the royal treasures, he would ensure that none were lost. f the king had a ring from the princess's finger thrown in the stream, it would show what his boasting was worth.
The individuals told the king that the prince claimed to safeguard the royal treasures if given control over them.  If the king threw a ring belonging to the princess into a river, it would prove or disprove his boast.