Yoreh Deah Siman 267 Seif 53

נג וּכְשֵׁם שֶׁהָאִשָּׁה אוֹמֶרֶת: בְּפָנַי נִכְתַּב וּבְפָנַי נֶחְתַּם, אִם הִתְנָה עָלֶיהָ, כֵּן הָעֶבֶד.

 

Seif 53

Just as the woman must say: “It was written and signed in my presence,” when it was stipulated that she do so, as we have explained in that context, the same applies for a servant/slave.