Yoreh Deah Siman 267 Seif 30

ל תָּלַשׁ בִּזְקָנוֹ וְדִלְדֵל בּוֹ עֶצֶם מֵהַלֶּחִי, יוֹצֵא לְחֵרוּת.

Seif 30

If the master pulls out the slaves beard and by doing so dislocates his jaw bone he is granted his freedom.