The Didache

On the Lord's own day, assemble in common to break bread and offer thanks; but first confess  your sins, so that your sacrifice may be pure.  However no one quarreling with your brother may join your meeting until they are reconciled; your sacrifice must not be defiled.  for here we have the saying of the Lord:  In every place and time offer me a pure sacrifice; for I am a mighty King. says the Lord; and my name spreads terror among the nations.