מדרש על זבחים 71:7

(Devarim 17:1) "You shall not sacrifice to the L-rd your G-d an ox or a sheep in which there is a blemish": R. Yehudah says: I might think that if one slaughtered a sin-offering in the south (instead of the north) he transgresses a negative commandment; it is, therefore, written "You shall not sacrifice to the L-rd your G-d a sin-offering in which there is a blemish. For (slaughtering a sin-offering with) a blemish he transgresses a negative commandment, but not for slaughtering it in the south. The sages say: Even for slaughtering a sin-offering in the south he transgresses a negative commandment.