הלכה על ויקרא 15:26

One who releases his slave transgresses a positive commandment (Lev 15:26) “forever you will make them work for you." it is permitted to free a slave for the sake of a Mitzvah, even a rabbinic one, for example if one was short a man in the synagogue for a making a minyan, if one only had 9 one should free his slave to make 10, and so forth. As well as a maid servant if it is customary for her to behave inappropriately with others we compel her master to free her, in order that the barrier be removed.