Since we have begun to speak of devils, we think it fitting to add certain facts, which are a warning to avoid their incantations and the counsels of those who have dealings with them. For they admit no one to learn their magic except those whom they rob of the honour of their Christianity by a horrible sacrilege. In a certain famous monastery a monk had been brought up from childhood and had attained to some knowledge of letters.

Whilst living in a cell attached to the church under the rule of his Abbot, he fell ill of a disease, through which, to his sorrow, he had occasion for talking with a Jew skilled in medicine. Gathering boldness from their intimacy, they began to reveal their secrets to one another. And so the monk, being curious about wicked arts and aware that the Jew understood magic, pressed him hard. The Jew consented and promised to be his mediator with the Devil. Time and place for a meeting are fixed.

At last he is brought by his intermediary into the presence of the Devil; he asks through the other to be admitted to a share in the teaching. That abominable ruler says it can by no means be done, unless he denies his Christianity and offers sacrifice to him. He asked what sacrifice.

“That which is pleasing in a man.”

“What is that?”

“You shall make a libation of your seed,” said he; “When you have poured that out to me, then you shall enjoy the reward of your sacrifice.”

Oh, crime! Oh, shameful act! And he of whom this was demanded was a priest! And this Thy ancient enemy did, O Lord, to cast the dishonour of sacrilege on Thy holy order and Thy Blessed Victim! Be not silent; restrain not Thy vengeance, Lord.

What shall I say? How shall I say it? The unhappy man did what was required of him, he whom Thou hadst abandoned, Ah, would it had been in time! And so with that horrible libation he declares his renunciation of his faith. But let me give one instance of the magic which he learnt by this accursed bargain.

He was in the habit of having intercourse with a certain nun. Moreover he lived in a cell with one monk as his companion, who had outside duties to perform, whilst he remained at home with leisure for his wickedness. One day, therefore, they were sitting in the cell, when his companion returned from his business, and when they saw him afar off, there was no escape open to the woman, but her flight would bring her into the path of the returning monk.

And so this new sorcerer, seeing his woman companion in a fright, said, “Go to meet the man as he comes, looking neither to the right nor to the left, and fear nothing.” The woman trusted him and went. But he stood in the doorway and with an incantation which he had learnt, turned her into a monstrous dog. When she came near the returning monk, he said, “Ha! Whence comes this great dog?” But she in much fear passed him by and knew by these words under what shape she had escaped.

Finally the monk coming to the house kept asking whence a dog of that size had come. “He belongs to that neighbour of ours,” said he. “Have you not seen him before?” And so the other was silent, guessing the truth. Living for a long time, therefore, without God, in the end, thanks be to God, he was stricken with a severe illness, and whether he would or not, had to confess what he had done.

The matter was referred to the judgment of wise men and chiefly to Anselm, afterwards Archbishop of Canterbury and then Abbot of Bec. Chiefly through his advice that most filthy profaner of the divine mysteries was cast out from administering them. Thus compelled to give up celebrating them, yet nothing could clear his mind of the belief that he would ere long be made a bishop; whereas he died not a prelate, but an unfrocked priest for evermore.

Source: Guibert of Nogent, De vita sua / Monodiae, Book II, chapter 5, in C. C. Swinton Bland, trans., The Autobiography of Guibert, Abbot of Nogent-sous-Coucy. London: George Routledge; New York: E. P. Dutton, 1925.