Rashi on Deuteronomy 23:7/רש"י על דברים כ״ג:ז׳

1לא תדרש שלמם THOU SHALT NOT SEEK THEIR PEACE [NOR THEIR GOOD] — Since it states, (v. 17) “He (the runaway slave) shall abide with you, even among you, … [where it shall be good for him]” one might think that this (a Moabite or Ammonite runaway slave) should also be treated likewise, therefore Scripture states לא תדרש שלמם THOU SHALT NOT SEEK THEIR PEACE [NOR THEIR GOOD] (Sifrei Devarim 251:2).