Babylonian Talmud, Gittin 45a

MISHNAH – captives should not be redeemed for more than their value, to prevent abuses. Captives should not be helped to escape, to prevent abuses. Rabban Simeon b. Gamaliel says [that the reason is] to prevent the ill-treatment of fellow captives. GEMARA. The question was raised: Does this prevention of abuses relate to the burden which may be imposed on the community or to the possibility that the activities [of the bandits] may be stimulated? — Come and hear: Levi b. Darga ransomed his daughter for thirteen thousand denarii of gold. Said Abaye: But are you sure that he acted with the consent of the Sages? Perhaps he acted against the will of the Sages.