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 VII

Canon VII.

Concerning those who have partaken at a heathen feast in a place appointed for heathens, but who have brought and eaten their own meats, it is decreed that they be received after they have been prostrators two years; but whether with oblation, every bishop must determine after he has made examination into the rest of their life.

Notes.

Ancient Epitome of Canon VII.

If anyone having his own food, shall eat it with heathen at their feasts, let him be a prostrator for two years.

Hefele.

Several Christians tried with worldly prudence, to take a middle course.  On the one hand, hoping to escape persecution, they were present at the feasts of the heathen sacrifices, which were held in the buildings adjoining the temples; and on the other, in order to appease their consciences, they took their own food, and touched nothing that had been offered to the gods.  These Christians forgot that St. Paul had ordered that meats sacrificed to the gods should be avoided, not because they were tainted in themselves, as the idols were nothing, but from another, and in fact a twofold reason:  1st, Because, in partaking of them, some had still the idols in their hearts, that is to say, were still attached to the worship of idols, and thereby sinned; and 2dly, Because others scandalized their brethren, and sinned in that way.  To these two reasons a third may be added, namely, the hypocrisy and the duplicity of those Christians who wished to appear heathens, and nevertheless to remain Christians.  The Synod punished them with two years of penance in the third degree, and gave to each bishop the right, at the expiration of this time, either to admit them to communion, or to make them remain some time longer in the fourth degree.