How we know that a Quorum is made of 10: Berachot 21b
Importance of a Quorum Vs. Set Times for Shema and Linking Prayers of Redemption and the Amidah: Rosh Berachot 1:1
The Importance of having a Quorum present on time for prayer: Berachot 6b
Having a quorum for a practice which is considered to involve "Holiness": Megillah 23b
Use of the phrase, "Dear ones," to refer to a quorum, specifically: Megillah 23b
Use of Gd's Name in a ritual, without a quorum: Megillah 23b