Deuteronomy 24:4

her former husband, which sent her away, may not take her again to be his wife after that she is defiled, for that is what her second marriage amounted to, so far as her first husband was concerned; it was implicitly equal to adultery; for that is abomination before the Lord; and thou shalt not cause the land to sin which the Lord, thy God, giveth thee for an inheritance, since such frivolous disregard of the sanctity of the marriage-tie was equivalent to unnatural sins of immorality and to incest, Leviticus 18:25. While divorce was thus permitted to the Jews, as the Lord says, on account of the hardness of their hearts, Matthew 19:8, yet remarriage, in the circumstances as noted, brought defilement upon the woman, and a remarriage of the first husband to the divorced woman was not permitted.