מדרש על בבא מציעא 118:14

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."