"In some provinces a difference in dress distinguishes the Jews or Muslims from the Christians, but in certain others such a confusion has grown up that they cannot be distinguished by any difference. Thus it happens at times that through error Christians have relations with the women of Jews or Muslims, and Jews and Muslims with Christian women. Therefore, that they may not, under pretext of error of this sort . . . we decree that such Jews and Muslims of both sexes in every Christian province and at all times shall be marked off in the eyes of the public from other peoples through the character of their dress. Particularly, since it may be read in the writings of Moses [Numbers 15:37-41], that this very law has been enjoined upon them."
Who said that? Leave your guess in the comments section below. Please, no google searches or cheating. Answer to follow in one week.
As one of you noted, this is from Canon 68 of the Fourth Lateran Council of 1215.