Now when Ezra had prayed, and when he had confessed, weeping and casting himself down before the house of God, there assembled unto him out of Israel a very great congregation of men and women and children: for the people wept very sore.  And Shechaniah the son of Jehiel, one of the sons of Elam, answered and said unto Ezra, “We have trespassed against our God, and have taken strange wives of the people of the land: yet now there is hope in Israel concerning this thing. Now therefore let us make a covenant with our God to put away all the wives, and such as are born of them, according to the counsel of my lord, and of those that tremble at the commandment of our God; and let it be done according to the law.  Arise; for this matter belongeth unto thee: we also will be with thee: be of good courage, and do it.” Ezra 10:1-4

Further reading: Ezra 9; 10; Leviticus 26:40-41; Isaiah 55:6-7; 2 Corinthians 6:17; 1 John 1:7-9