Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon LXXXIV

p. 402 Canon LXXXIV.

Following the canonical laws of the Fathers, we decree concerning infants, as often as they are found without trusty witnesses who say that they are undoubtedly baptized; and as often as they are themselves unable on account of their age to answer satisfactorily in respect to the initiatory mystery given to them; that they ought without any offence to be baptized, lest such a doubt might deprive them of the sanctification of such a purification.

Notes.

Ancient Epitome of Canon LXXXIV.

Whoever do not know nor can prove by documents that they have been baptized, let them be christened.

This is canon VII., of the Sixth Council of Carthage, (Vide Hefele, Hist. of the Councils, Vol. II., p. 424); and Canon lxxv., of the African code (to which Balsam on attributes this canon), by the Greek numbering, (lxxii. by the Latin).