source?
???? ??????? ??? ???? ??????, Gittin 88b ?????? ??? ???? ???”?, Rashi Shemos 21:1, Shulchan Aruch Choshen Mishpat 26:1, Rama, Tashbetz Tur 3:6, Kesph Hakadashim 26:1.
Chazon Ish Sanhedrin 15:4, Divray Malkiel 5:210, Pamoney Zahav 26, Igros Moshe 1:58, Tzizt Eliezer 11:93.
In fact, the Chazon Ish writes that it is even a greater Chillul Hashem for Jewish judges to rule in accordance with non-Jewish law instead of Halacha.