Canon 33 of the Council of Elvira (305)
“It has seemed good to absolutely forbid the bishops, the priests, and the deacons, i.e., all the clerics in the service of the sacred ministry, to have relations with their wives and procreate children; should anyone do so, let him be excluded from the honor of the clergy.”
The Spanish Synod of Elvira, occurring eight years before the Edict of Milan and twenty-years before Nicaea, represents the first time we see the law of continence specifically spelled out canonically. Continence is mandated for all Major Orders - deacon, priest, bishop - and it is made explicitly clear that this applies to married clerics in a particular way. Neither this synod nor any subsequent councils suggest they are promulgating novelty. Elvira and succeeding synods state that they are simply reaffirming existing tradition.
Canon 29 of the First Council of Arles (314)
“Moreover, concerned with what is worthy, pure, and honest, we exhort our brothers in the episcopate to make sure that priests and deacons have no [sexual] relations with their wives, since they are serving the ministry everyday. Whoever will act against this decision will be deposed from the honor of the clergy.”
Notice how continence is linked to the permanent ministerial activity of the cleric, as we saw with Tertullian and Origen.