Second Council of Nicaea, Canon VII

That to churches consecrated without any deposit of the reliques of the Saints, the defect should be made good.

Paul the divine Apostle says:  “The sins of some are open beforehand, and some they follow after.”  These are their primary sins, and other sins follow these.  Accordingly upon the heels of the heresy of the traducers of the Christians, there followed close other ungodliness.  For as they took out of the churches the presence of the venerable images, so likewise they cast aside other customs which we must now revive and maintain in accordance with the written and unwritten law.  We decree therefore that relics shall be placed with the accustomed service in as many of the sacred temples as have been consecrated without the relics of the Martyrs.  And if any bishop from this time forward is found consecrating a temple without holy relics, he shall be deposed, as a transgressor of the ecclesiastical traditions.

Translation: Henry R. Percival, The Seven Ecumenical Councils, NPNF II.14 (1900), via CCEL.