WSC Q.72: What is forbidden in the seventh commandment?
The seventh commandment forbiddeth all unchaste thoughts, words, and actions. (Matt. 15:19, Matt. 5:28, Eph. 5:3–4)
WLC Q.139: What are the sins forbidden in the seventh commandment?
The sins forbidden in the seventh commandment, besides the neglect of the duties required, (Prov. 5:7) are, adultery, fornication, (Heb. 13:4, Gal. 5:19) rape, incest, (2 Sam. 13:14, 1 Cor. 5:1) sodomy, and all unnatural lusts; (Rom. 1:24,26–27, Lev. 20:15–16) all unclean imaginations, thoughts, purposes, and affections; (Matt. 5:28, Matt. 15:19, Col. 3:5) all corrupt or filthy communications, or listening thereunto; (Eph. 5:3–4, Prov. 7:5,21–22) wanton looks, (Isa. 3:16, 2 Pet. 2:14) impudent or light behaviour, immodest apparel; (Prov. 7:10,13) prohibiting of lawful, (1 Tim. 4:3) and dispensing with unlawful marriages; (Lev. 18:1–21, Mark 6:18, Mal. 2:11–12) allowing, tolerating, keeping of stews, and resorting to them; (1 Kings 15:12, 2 Kings 23:7, Deut. 23:17–18, Lev. 19:29, Jer. 5:7, Prov. 7:24–27) entangling vows of single life, (Matt. 19:10–11) undue delay of marriage, (1 Cor. 7:7–9, Gen. 38:26) having more wives or husbands than one at the same time; (Mal. 2:14–15, Matt. 19:5) unjust divorce, (Mal. 2:16, Matt. 5:32) or desertion; (1 Cor. 7:12–13) idleness, gluttony, drunkenness, (Ezek. 16:49, Prov. 23:30–33) unchaste company; (Gen. 39:19, Prov. 5:8) lascivious songs, books, pictures, dancings, stage plays; (Eph. 5:4, Ezek. 23:14–16, Isa. 23:15–17, Isa. 3:16, Mark 6:22, Rom. 13:13, 1 Pet. 4:3) and all other provocations to, or acts of uncleanness, either in ourselves or others. (2 Kings 9:30, Jer. 4:30, Ezek. 23:40)