Midrash for Bava Metzia 118:18

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.

We are taught in a Baraitha: R. Eliezer the Great said: "Why does the Scripture in thirty-six, according to others in forty-six places, warn concerning strangers? Because his original character is bad [into which ill treatment might cause him to relapse]." Why is there added (Ex. 22, 20) For strangers ye were in the land of Egypt? We are taught in a Baraitha: R. Nathan says: "Do not reproach thy neighbor with a fault which is also thine own;" and this is what people say: "To him who has had a hanged one in his family, do not even mention hang up a fish."