Early Church Fathers
7 Conc. Trid sessio xxiv. De Matr., can. x. It is curious to note that while Eustathius and his followers held all marriage to be sinful, Luther (at least at one time) taught that it was a sin for anyone to remain unmarried who could "increase and multiply!" The Synod of Gangra in this canon sets forth the unchanging position of the Cathoilc Church upon this point.
1 Vide their edition of Opp. S. Leonis M., Tom. III., pp. 124, 685, 755.