1 Corinthians 7:3 – 5
New International Version (NIV1984)
3 The husband should fulfill his marital duty to his wife, and likewise the wife to her husband. 4 The wife’s body does not belong to her alone but also to her husband. In the same way, the husband’s body does not belong to him alone but also to his wife. 5 Do not deprive each other except by mutual consent and for a time, so that you may devote yourselves to prayer. Then come together again so that Satan will not tempt you because of your lack of self-control.
From BibleGateway.com: http://www.biblegateway.com/passage/?search=1 Corinthians 7:3 – 5&version=NIV1984