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 52Canon XXIX.

If anyone who is excommunicated shall receive communion before his cause is heard he brings damnation on himself.

Likewise it pleased the whole Council that he who shall have been excommunicated for any neglect, whether he be bishop, or any other cleric, and shall have presumed while still under sentence, and his cause not yet heard, to receive communion, he shall be considered by so doing to have given sentence against himself.