BabylonianTalmud, Baba Batra 8a - 2

R. Assi further said in the name of R. Yohanan: All are required to contribute to the repair of the town walls, including orphans, but not the Rabbis, because the Rabbis do not require protection. R. Papa said: For the repair of the walls, for the horse-guard and for the keeper of the armory even orphans have to contribute, but the Rabbis [do not, since they] do not require protection. The general principle is that even orphans have to contribute for any public service from which they derive benefit. Rabbah levied a contribution for charity on the orphans of the house of Bar Merion; whereupon Abaye said to him: Has not R. Samuel b. Judah laid down that money for charity is not to be levied on orphans even for the redemption of captives? — He replied: I collect from them in order to give them a better standing. [Soncino translation]