Although we learned above that it is considered a violation of a positive commandment for the owner of an eved kena’ani – a non-Jewish slave – to free him because of the pasuk, “Le-olam ba-hem ta’avodu – you should subjugate them forever,” (see Vayikra 25:46), our Gemara discusses a number of cases where the activities of the owner is understood as a statement that he is freeing his slave. For example, Rabbi Yehoshua ben Levi teaches that when a slave owner leaves a set of tefillin for his eved kena’ani, it is an indication that the slave is set free.
Although as we have mentioned, an eved kena’ani is obligated in many mitzvot, he is not obligated to put on tefillin, since his only obligation is to perform those mitzvot that women are commanded to perform. Although a woman can perform mitzvot that she is not obligated to do on a voluntary basis, nevertheless it is out of the ordinary for an eved to do so. Thus, leaving him tefillin is understood as a statement on the part of the owner that this man is no longer an eved.
Another case presented by the Gemara is the statement made by Rav Shmuel bar Yehuda quoting Rabbi Yohanan that a person on his deathbed who says, “That slave was very kind to me (nahat ru’ah astah li), she should be dealt with kindly,” is listened to, and the people who inherit are forced to deal with her kindly. The Gemara explains that this ruling stems from the common law of mitzva le-kayyem divrei ha-met: that we are obligated to fulfill the expressed desires of someone who dies.
Rashi understands that the expression that she should be dealt with kindly means that we must offer her whatever will satisfy her; if she insists on her freedom, the heirs will be obligated to set her free. Some of the rishonim object to this interpretation, arguing that an unclear statement on the part of the dead man should not force his heirs to free the slave, something forbidden by the Torah. The Ramban and others respond that as long as there is a good reason for freeing the slave, it is permissible (see daf 38). Nevertheless, many of the rishonim disagree with Rashi and say that the heirs are not obligated to do anything beyond offering her a comfortable job – as a slave.