I've been spending some time interacting with a Roman Catholic on various Luther related issues. She used this quote:
Moses is an executioner, a cruel lictor, a torturer who tears our flesh out with pincers . . Whoever, in the name of Christ, terrifies and troubles consciences, is not the messenger of Christ, but of the devil . . Let us send Moses packing and forever.
So far, I've only found this quote being used one other place: the Romanist propaganda page entitled, "Luther Exposing the Myth". I've interacted with this web page before, though never the author directly: Raymond Taouk. I wrote the host web page a few years ago and let them know I critiqued some of Mr. Taouk's research, and they told me they forwarded that on to him. I never received any response from him. "Luther Exposing the Myth" is a popular web page utilized by zealous Romanists.
Taouk documents the quote as D. Martini Lutheri Exegetica Opera Latina, published by Elsperger (Erlangen, Heyder, 1829-84), Vol. 18 pg. 146. I doubt Mr. Taouk actually utilized this Latin text. I was not though, able to determine exactly which secondary source Taouk used.
The caricature presented by Taouk is that Luther despised Moses and slandered Moses. The context though says something quite different. This quote is found in LW 12:207, 211. Luther is commenting on Psalm 45:2. It is a comparison is between "King" Moses and the Law (imperfect) and "king" Jesus and the Gospel. The first part: "Moses is an executioner, a cruel lictor, a torturer who tears our flesh out with pincers . ." is found on page 207:
This is the first sweet and delightful thing in this lyric, which sings about and promises a kingdom with such a King. There will be no imperfections in Him, but a will full of virtues and a mind full of wisdom, with glowing love toward all miserable, damned, and sorrowful sinners. Moses is not such a king. He is a tormentor and cruel executioner and torturer, who torments us and troubles us with his terrors, threatenings, and displays of wrath. He forces us to do good outwardly; or, if we do our best, he inwardly humbles us and makes us long for grace. But our King, who is celebrated here, is full of mercy, grace, and truth. In Him love for mankind is to be found and the greatest sweetness; a person who, as we find in Isaiah 42:2, “does not cry in the streets,” is not austere and rough, but patient and long-suffering. He exercises judgment against the wicked and blasphemers, and shows mercy toward sinners. Therefore He is a most pleasant and fair King, and there is no one like Him in the whole world. In Him is to be found the highest virtue and the highest love toward God and men. It is with these adornments that His person is decorated, so that there is no overweening pride, desire, lust, or any other base affection in Him. We see Him described this way in the Gospels, and the facts themselves point to His having been so. He did not keep company with the holy, powerful, and wise, but with despicable and miserable sinners, with those ruined by misfortune, with men weighed down by painful and incurable diseases; these He healed, comforted, raised up, helped. And at last He even died for sinners. He did not frighten, and He did not kill, as Moses did, but He drew, gladdened, comforted, cured, and aided all who came to Him. He is therefore the King of kings, without equal. Yet this is true only if you look at the spirit and not at the external appearance of the flesh. This is simply one aspect of the description of His person, pointed out briefly and with few words. The holy Evangelists and St. Paul in his Epistles describe it more fully and enlarge upon it; they paint this King in His true colors and point out what kind of person He is, and these things are most helpful for those of us who find ourselves in difficulties and vexations of conscience.
The second part: "Whoever, in the name of Christ, terrifies and troubles consciences, is not the messenger of Christ, but of the devil . . Let us send Moses packing and forever" is found here: LW 12:211
So Christ should not be depicted with gall or a sword in His mouth, as they always portray Him, unless it is to be understood spiritually. He should be depicted in such a way that His lips seem to be pure sugar or honey. Whoever depicts His mouth otherwise errs, and we should rather listen to this poet than to the papists and Satan, the authors of this horrible picture. For this poet will not deceive us when he ascribes to Christ the loveliest mouth. This must be noted carefully. For Christ should not make hearts sad with His words, He ought not to terrify. Whoever terrifies and vexes consciences in Christ's name is not a messenger of Christ but of the devil, for Christ's name is: "A bruised reed He will not break, and a dimly burning wick He will not quench." He is gentle: "He will not cry or lift up His voice or make it heard in the street" (Is. 42:3, 2). He is not rough, severe, biting like Moses, who looks like the very devil and speaks in a way that our heart almost vanishes before him. For he has lips overflowing with gall and wrath, that have been embittered with laurel and gall, in fact, with hellish fire. So away forever with Moses! But our King has pleasant lips; that is, His Word is the Word of the remission of sins and of comfort for the lowly, the Word of life and salvation to recall the damned and dying.