1 Corinthians 7:5

Defraud ye not one the other. By denying the marriage debt. The words and to fasting, though in the Greek, are wanting in the Latin. Hence Nicholas I., in his answers to the questions if the Bulgarians (c. 50), writes to them that, throughout the forty days of Lent, they should not come at their wives. But this is a matter of counsel.

And come together again. From this Peter Martyr and the Magdeburgians conclude that it is not lawful for married persons to vow perpetual continence by mutual consent. But the answer to this is that the Apostle is not prescribing but permitting the marriage act.