Reference for Avodah Zarah 1:2
רַבִּי יִשְׁמָעֵאל אוֹמֵר, שְׁלשָׁה יָמִים לִפְנֵיהֶם וּשְׁלשָׁה יָמִים לְאַחֲרֵיהֶם, אָסוּר. וַחֲכָמִים אוֹמְרִים, לִפְנֵי אֵידֵיהֶן אָסוּר, לְאַחַר אֵידֵיהֶן מֻתָּר:
R. Yishmael says: Three days before and three days afterwards it is forbidden, and the sages say: Before their festivals it is forbidden and afterwards it is permitted. [And this is the halachah. And in the exile where we cannot prevent ourselves from dealing with them, their being the major source of our livelihood, and also, because we fear them, only their festival day itself is forbidden. And today it is regarded as permitted even on the day itself, the rabbis taking it for granted that they do not go and thank (their god); for all that is forbidden in this tractate obtains with actual idolators and idolatry only.]