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 CXXXI

Canon CXXXI.  (Greek CXXXII.)

Who should be allowed to give evidence.

They who are forbidden to be admitted as accusers are not to be allowed to appear as witnesses, nor any that the accuser may bring from his own household.  And none shall be admitted to give witness under fourteen years of age.

Notes.

Ancient Epitome of Canon CXXXI.

And whoso is not past fourteen years of age [is not to give witness].  An accuser is not to produce witnesses from his own house.

Johnson.

See Can. 129.