פירוש על קידושין 127:11

R. Ashi uses a verse to prove that a father has the right to prohibit a daughter by making a statement concerning her marriage. The words “I gave my daughter to a man” would prohibit her to everyone. After all, we would not know who married her. The word “this” frees her to be with that man (and after his death or divorce, with any other). This is all accomplished by a mere statement.
However, the father does not have any power to forbid his daughter to the priesthood by declaring that she was taken captive. Therefore, he is not believed.