You cover the altar of the LORD with tears, with weeping and with groaning, because He no longer regards the offering or accepts it with favor from your hand. Yet you say, “For what reason?” Because the LORD has been a witness between you and the wife of your youth, against whom you have dealt treacherously, though she is your companion and your wife by covenant. But not one has done so who has a remnant of the Spirit…Take heed then to your spirit, and let no one deal treacherously against the wife of your youth. “For I hate divorce,” says the LORD. (Malachi 2:13-16).
Everyone who divorces his wife and marries another commits adultery; and he who marries one who is divorced from a husband commits adultery. (Luke 16:18).
For the married woman is bound by law to her husband while he is living; but if her husband dies, she is released from the law concerning the husband. So then if, while her husband is living, she is joined to another man, she shall be called an adulteress; but if her husband dies, she is free from the law, so that she is not an adulteress, though she is joined to another man. (Romans 7:2-3).
See also Matthew 5:31-32, 19:3-9.