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

p. 405 Canon XCIV.

The canon subjects to penalties those who take heathen oaths, and we decree to them excommunication.

Notes.

Ancient Epitome of Canon XCIV.

Whoever uses Gentile oaths, is worthy of punishment, for he is cut off.

The reference is to canon lxxxj. of St. Basil’s canons.

Van Espen.

Tertullian (De Idolatria, cap. xx.) supposes that to swear by the false gods of the Gentiles, contains in itself some idolatry, an opinion shared by St. Basil, comparing those using such oaths with them who betrayed Christ, and who are partakers of the talk of devils.