Yoreh Deah Siman 267 Seif 41

מא כֵּיצַד בִּשְׁטָר, כּוֹתֵב עַל הַנְּיָר אוֹ עַל הַחֶרֶס: הֲרֵי אַתָּה בֶּן חוֹרִין, אוֹ הֲרֵי אַתָּה לְעַצְמְךָ, אוֹ אֵין לִי עֵסֶק בְּךָ, וּמוֹסְרוֹ לְיָדוֹ אוֹ לְאַחֵר בִּשְׁבִילוֹ, אֲפִלּוּ בְּלֹא יְדִיעַת הָעֶבֶד, שֶׁזְּכוּת הוּא לוֹ שֶׁיֵּצֵא מִתַּחַת יַד רַבּוֹ לְחֵרוּת, וְאִם מוֹחֶה בְּיָדוֹ מִלְּקַבְּלוֹ, לֹא יָצָא בּוֹ לְחֵרוּת.

 

Seif 41

How does a slave achieve his freedom through the transfer of a legal document? The master must write to him on a paper or on a shard: “Behold, you are a free man,” “Behold, you are your own property,” “I no longer have anything to do with you,” And handed over to him or to another for him, Even without the knowledge of the slave because it is benefit to him to be freed from under the master’s hand to freedom, however if he protests when he receives it he does not go free.