“With all our strength, therefore, let us never receive communion from or grant it to heretics; ‘Give not that which is holy unto dogs, saith the Lord, neither cast ye your pearls before swine,’ (Matt. 7:6); lest we become partakers in their dishonor and condemnation.” St. John Damascene   (Patrologia Graeca, vol. 94, col. 1149, 1152, 1153; Also De Fide Orthodoxa (Exposition of the Orthodox Faith), Book IV, Chapter XIII).