Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Synods of Sardica, Carthage, Constantinople, and Carthage Under St. Cyprian, Which Canons Were Received by the Council in Trullo and Ratified by II. Nice.: Canon XX

Canon XX.  (Greek xxiii.)

Of accused presbyters or clerks.

But if presbyters or deacons shall have been accused, there shall be joined together from the neighbouring places with the bishop of the diocese, the legitimate number of colleagues, whom the accused shall seek from the same; that is together with himself six in the case against a presbyter, in that against a deacon three.  They shall discuss the causes, and the same form shall be kept with regard to days and postponements and removals from communion, and in the discussion of persons between the accusers and the accused.

But the causes of the rest of the clergy, the bishop of the place shall take cognizance of and determine alone.

Notes.

Ancient Epitome of Canon XX.

When a presbyter is accused, six of the neighbouring bishops together with the bishop of that region shall judge the matter.  But for a deacon, three.  What things concern the other clerics even one bishop shall examine.

This is Canon viii. of Hippo, 393.

Johnson.

See Canon 12.