Yoreh Deah Siman 267 Seif 47

מז כָּל שְׁטָר שֶׁיֵּשׁ עָלָיו אֲפִלּוּ עֵד אֶחָד כּוּתִי, פָּסוּל, חוּץ מִגִּטֵּי נָשִׁים וְשִׁחְרוּרֵי עֲבָדִים שֶׁהֵם כְּשֵׁרִים בְּעֵד אֶחָד יִשְׂרָאֵל וְעַד אֶחָד כּוּתִי, וְהוּא שֶׁיִּהְיֶה כּוּתִי חָבֵר. וּבַזְּמַן הַזֶּה שֶׁהַכּוּתִים כְּגוֹיִים לְכָל דִּבְרֵיהֶם, אָנוּ לְמֵדִים מֵהֶם לַצְּדוֹקִים, שֶׁהַצְּדוֹקִים בַּזְּמַן הַזֶּה כְּמוֹ כּוּתִים בְּאוֹתוֹ זְמַן, קֹדֶם שֶׁגָּזְרוּ עֲלֵיהֶם שֶׁיִּהְיוּ כְּגוֹיִים.

Seif 47

Any legal document that is signed by even one witness who is a cuthean is not acceptable, with the exception of bills of divorce for women and bills of release for slaves, provided the Cuthean is known to be precise in his observance.

In the present age, when the Cutheans are considered as gentiles with regard to all matters, we apply the laws stated with regard to them to the Sadducees. For the Sadducees in the present era are considered like the Cutheans of the previous era, before it was decreed that they would be considered like gentiles.