19 Again, I tell you the truth, if two of you on earth agree about whatever you ask, my Father in heaven will do it for you. 20 For where two or three are assembled in my name, I am there among them.” 21 Then Peter came to him and said, “Lord, how many times must I forgive my brother who sins against me? As many as seven times?” 22 Jesus said to him, “Not seven times, I tell you, but seventy-seven times! 23 “For this reason, the kingdom of heaven is like a king who wanted to settle accounts with his slaves.
Berakhot 6aBabylonian Talmud
And from where is it derived that ten people who pray, the Divine Presence is with them? As it is stated: “God stands in the congregation of God,” and the minimum number of people that constitute a congregation is a quorum of ten. From where is it derived that three who sit in judgment, the Divine Presence is with them? It is derived from this same verse, as it is stated: “In the midst of the judges He judges,” and the minimum number of judges that comprises a court is three.
Notes and References
"... In Matthew 18:20, it is written, 'Where two or three are gathered in my name, thjere I am in the midst of them'; compare this to the passage in the Talmud, where the sages state, 'From where is it derived that three who sit in judgment, the Divine Presence is with them?' ..."
Patterson, David Genocide in Jewish Thought (pp. 75-76) Cambridge University Press, 2012