Midrash su Proverbi 21:27

3) [(Vayikra 1:2): "A man, if he offer of you, a sacrifice to the L–rd"] "A man" — to include proselytes; "of you" — to exclude heretics. Why do you see it that way? Why not: "A man" — to include heretics; "of you" — to exclude proselytes? After Scripture includes, it excludes, viz. (Vayikra 1:2): "the children of Israel." Just as the children of Israel are accepters of the covenant, so proselytes — to exclude heretics, who do not accept the covenant. — But why not say: Just as the children of Israel are children of accepters of the covenant, so, heretics — to exclude proselytes, who are not! It is, therefore, written "of you" (i.e., like you, in your deeds). So that, perforce, we must understand it as: Just as Israel are accepters of the covenant, so, proselytes — to exclude heretics, who are not, having broken the covenant. And thus is it written (Mishlei 21:27): "The sacrifice of the wicked is an abomination."

4) "A man, if he offer, etc." I might think this is a decree (i.e., that he must do so), it is, therefore, written "if he offer" — it is optional. (Mishlei 21:27): "a sacrifice (korban) to the L–rd" — he must sanctify it (by saying "This is a burnt-offering") before offering it up, (thus rendering it a "korban" before he actually sacrifices it). These are the words of R. Yehudah. R. Shimon said: Whence is it derived that one should not say: "To the L–rd, a burnt-offering," "To the L–rd, a meal-offering," "To the L–rd, peace-offerings?" From "a sacrifice (korban) to the L–rd." Now is this not a kal vachomer? If in respect to what is destined to be sanctified, Scripture states that the name of Heaven is to be mentioned only after "korban" (to forestall the possibility of its being mentioned in vain by his saying "To the L–rd," and not following up with "korban") — how much more so must the name of Heaven not be mentioned in vain (in mundane circumstances)!