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 CXXX

p. 505 Canon CXXX.  (Greek cxxxi.)

That he who has failed to prove one charge shall not be allowed to give evidence to another.

So, too, it seemed good that as often as many crimes were laid to clerics by their accusers, and one of the first examined could not be proved, 484 they should not be allowed to go on giving evidence on the other counts.

Ancient Epitome of Canon CXXX.

He who makes many accusations and proves nothing [is not to give witness].

Footnotes

The Latin here is evidently corrupt.