How did Erkang get the silver pearl powder?

In Princess Pearl III, Erkang was captured by the princess when he went out to war. Because the princess saw Erkang's fine features and kung fu, she wanted to keep him as her husband. Erkang was badly hurt. In order to alleviate Erkang's pain and better control Erkang, she promised to be her husband, so the princess took silver pearl powder to Erkang for blackmail.