Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV: The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XXXVII
It is not lawful to receive portions sent from the feasts of Jews or heretics, nor to feast together with them.