Theodoret of Cyrus: Ordinary Marital Relations Chaste

And the holiness without which no one will see the Lord. By holiness he referred to self-control; it is possible even for those in wedlock to achieve it: Let marriage be held in honor and the marriage bed be undefiled; God will judge fornicators and adulterers.

- Theodoret of Cyrus (around A.D. 393 to around A.D. 457), Commentary on Hebrews, Chapter 12, in Theodoret of Cyrus, Commentary on the Letters of St. Paul, Volume 2, p. 190 (2001), Robert C. Hill translator.