Reference for Rosh Hashanah 16:2

ת"ר כי חק לישראל הוא משפט לאלהי יעקב מלמד שאין ב"ד של מעלה נכנסין לדין אא"כ קידשו ב"ד של מטה את החדש

Our Rabbis taught: 'For it is a statute for Israel, an ordinance for the God of Jacob': this teaches that th heavenly Beth din does not assemble for judgment until the Beth din on earth has sanctified the month'. Another [Baraitha] taught: 'For it is a statute for Israel'; this tells me only that Israel [are judged]; ho know that this applies also to the [other] nations of this world? Because it is written, an ordinance for the God of Jacob'.

Jastrow