Exodus 21:10

If he take him another wife; her food, her raiment, and her duty of marriage, shall he not diminish.

Cross-reference

1 Corinthians 7:1-6 discusses marital duties, echoing the requirement not to diminish food, clothing, and conjugal rights.

1 Corinthians 7:3 speaks of conjugal rights, directly paralleling the 'duty of marriage' in Exodus.