וְכֵ֤ן תַּֽעֲשֶׂה֙ בְּשִׁבְעָ֣ה בַחֹ֔דֶשׁ מֵאִ֥ישׁ שֹׁגֶ֖ה וּמִפֶּ֑תִי וְכִפַּרְתֶּ֖ם אֶת־הַבָּֽיִת׃
And so thou shalt do on the seventh day of the month for every one that erreth, and for him that is simple; so shall ye make atonement for the house.
Mishnah Shabbat
And these are of halakhot which they stated in the upper chamber of Hananiah ben Hezekiah ben Gurion, when they went up to visit him. They took a count, and Bet Shammai outnumbered Beth Hillel and on that day they enacted eighteen measures.