Rashi on Exodus 22:20/רש"י על שמות כ״ב:כ׳

1וגר לא תונה — means, do not vex him with words (referring to the fact that he is a stranger); contrarier in old French Similar is, (Isaiah 49:26) “And I will feed them that vex thee (מוניך) with their own flesh”.

2ולא תלחצנו NOR OPPRESS HIM — by robbing him of money (Mekhilta).

3כי גרים הייתם FOR YE WERE STRANGERS — If you vex him he can vex you also by saying to you: “You also descend from strangers”. Do not reproach thy fellow-man for a fault which is also thine (Mekhilta). Wherever גר occurs in Scriptures it signifies a person who has not been born in that land (where he is living) but has come from another country to sojourn there.