Ten bad spies and two good spies. - adat ra, "evil congregation," a congregation is ten
Why does "public sanctification" of God's name require a minyan?
Why is it important to pray with a minyan?
Nine rabbis do not constitute a minyan, but ten cobblers can.
How is it possible to count nine plus an open ark for minyan?
Rabbi Michael Leo Samuel - Historic Precedent
On the other hand, there are other rabbinical passages dating back to the Gaonic era (8th-10th centuries) that in Palestine, a minyan may have consisted of seven or six people.
The liturgical historian Abraham Milgram notes that after WWII, a number of Jewish communities actually went back to counting six or seven people as a “minyan,” until the time their ranks would grow in number. This specifically happened in the city of Dubrovnik, Yugoslavia
Rabbi Barry Leff - Ruling for Temple Beth-El on Nine and the Open Ark for a Minyan
There is an established custom at Temple Beth-El to count nine plus the open ark for a minyan. I considered whether it was necessary to abandon this custom that pre-dated my tenure here.
- The sources are clear that a minyan is ten; while there are sources that speak of nine plus a Torah or minor, those sources are not the generally accepted halacha.
- Requiring a minyan for devarim sh'b'kedusha is a rabbinic requirement, not a biblical ordinance. There is historical precedent for counting fewer than ten for a minyan in a time of urgent need.
- For a mourner saying kaddish is an "urgent need." For purposes of allowing mourners to say kaddish, we will allow counting nine plus a sefer Torah (open ark).
- Even though the principle of לא פלוג would suggest that if we count nine in this fashion for a minyan we should count it for all purposes, since the urgent need is for mourner's kaddish, and we don't want to convey the erroneous view that nine constitutes a minyan, we only permit using the Sefer Torah as the tenth for mourner's kaddish. Other forms of sanctification (e.g., repetition of the Amidah, barchu, etc.) require ten Jews above bar/bat mitzvah age.