They say to him, “Why then did Moses command to give her a certificate of divorce, and to send her away?”a Bible other translations
From Deut. 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.

Commentary for: Matthew 19:7