Midrash sa Levitico 19:33: Sifra & Ein Yaakov (Glick Edition)

1) (Vayikra 19:33) ("And if there dwell among you a stranger (i.e., a proselyte) in your land, you shall not oppress him.") If one came and said; I am a proselyte, I might think that he is to be accepted (as such); it is, therefore, written "among you" — when he is acknowledged among you (to be a proselyte). If he comes along with his witnesses (that he is a proselyte), whence is it derived (that he is to be accepted)? From "And if there dwell, etc." "in your land": This tells me (that they are accepted) only in Eretz Yisrael. Whence do I derive (the same) for outside the land? From "among you" — wherever you are. If so, why is it written "in your land"? In your land he must bring proof (that he is a proselyte); outside the land he need not bring proof.

2) "you shall not oppress him": You shall not say to him: "Yesterday you were an idolator, and today you have entered under the wings of the Shechinah!"

Our Rabbis were taught: He who annoys a stranger transgresses three negative commandments, and he who oppresses him transgresses two. Let us see, Regarding annoying, there are three negative commandments, (Ex. 22, 20; Lev. 19, 33 and 25, 17). If so, then there are three negative commandments concerning oppression also (namely, Ex. 22, 20; 23, 9 and 22, 24) — which include also the stranger. We must therefore say that in both cases, he transgresses three negative commandments.