Quoted from Deuteronomy 24:1.
“command.” The hard-hearted Pharisees used the word “command,” emphasizing their belief that if a woman committed adultery the husband had to divorce her. Jesus gently corrected their belief by saying Moses “allowed” (or “permitted”) divorce (Matt. 19:8), but it certainly was not a command. Many marriages have been healed even though one spouse committed adultery.