Nicæa I: canon XVIII

It has come to the attention of this holy and great synod that in some places and cities deacons give communion to presbyters, although neither canon nor custom allows this, namely that those who have no authority to offer should give the body of Christ to those who do offer. Moreover it has become known that some of the deacons now receive the eucharist even before the bishops. All these practices must be suppressed. Deacons must remain within their own limits, knowing that they are the ministers of the bishop and subordinate to the presbyters. Let them receive the eucharist according to their order after the presbyters from the hands of the bishop or the presbyter. Nor shall permission be given for the deacons to sit among the presbyters, for such an arrangement is contrary to the canon and to rank. If anyone refuses to comply even after these decrees, he is to be suspended from the diaconate.