The 56th prohibition is that we are forbidden from ever offering peace to the nations of Ammon or Moav. This ["offering peace"] refers to G‑d's command that before attacking any cities, we should first offer its inhabitants to give in and surrender to us. If they surrender the city, we are prohibited from attacking and killing them, as explained in Positive Commandment 190. The exceptions are Ammon and Moav, to whom we may not make this offer. G‑d prohibited us from offering the option of surrender and asking them to give in.1

The source of this prohibition is G‑d's statement2 (exalted be He), "You must never seek peace with them nor their well-being [as long as you exist]."

The Sifri3 says, "From the verse,4 'When you approach a city to wage war against it, you must propose a peaceful settlement,' one could think the same applies here [to Ammon and Moav]. The Torah therefore says, 'You must never seek peace with them nor their well-being.' But from the phrase,5 '[He must be allowed to live alongside you wherever he chooses in your settlements,] be good to him,' one could think the same applies here.6 The Torah therefore says, '[nor their well-being] as long as you exist.' "7