מדרש על מגילה 4:3

The intercalation takes place in the presence of three; Rabbi Eliezer says that ten (men are required), as it is said, "God standeth in the congregation of God" (Ps. 82:1), and if they become less than ten, since they are diminished they place a scroll of the Torah before them, and they are seated in a circle in the court-room, and the greatest (among them) sits first, and the least sits last; and they direct their gaze downwards to the earth and (then) they stand and spread out their hands before their Father who is in heaven, and the chief of the assembly proclaims the name (of God), and they hear a Bath Ḳol (saying) the following words, "And the Lord spake unto Moses and Aaron… saying, This month shall be unto you" (Ex. 12:1, 2).