The twenty-fourth of the wisdom sayings in Chapter 24 of St Benedict's Rule is, Not to hold guile in one's heart.
From St Gregory the Great's Dialogues, Chapter 8 of Book II:
"When as the foresaid monasteries were zealous in the love of our Lord Jesus Christ, and their fame dispersed far and near, and many gave over the secular life, and subdued the passions of their soul, under the light yoke of our Saviour: then (as the manner of wicked people is, to envy at that virtue which themselves desire not to follow) one Florentius, Priest of a church nearby, and grandfather to Florentius our sub-deacon, possessed with diabolical malice, began to envy the holy man's virtues, to back-bite his manner of living, and to withdraw as many as he could from going to visit him.
When he saw that he could not hinder his virtuous proceedings, but that, on the contrary, the fame of his holy life increased, and many daily, on the very report of his sanctity, took themselves to a better state of life : burning more and more with the coals of envy, he became far worse; and though he desired not to imitate his commendable life, yet fain he would have had the reputation of his virtuous conversation.
In conclusion so much did malicious envy blind him, and so far did he wade in that sin, that he poisoned a loaf and sent it to the servant of almighty God, as it were for a holy present. The man of God received it with great thanks, yet not ignorant of that which was hidden within. At dinner time, a crow daily used to come to him from the next wood, which took bread at his hands; coming that day after his manner, the man of God threw him the loaf which the Priest had sent him, giving him this charge: "In the name of Jesus Christ our Lord, take up that loaf, and leave it in some such place where no man may find it." Then the crow, opening his mouth, and lifting up his wings, began to hop up and down about the loaf, and after his manner to cry out, as though he would have said that he was willing to obey, and yet could not do what he was commanded.
The man of God again and again bide him, saying: "Take it up without fear, and throw it where no man may find it." At length, with much ado, the crow took it up, and flew away, and after three hours, having dispatched the loaf, he returned again, and received his usual allowance from the man of God.
But the venerable father, perceiving the Priest so wickedly bent against his life, was far more sorry for him than grieved for himself. And Florentius, seeing that he could not kill the body of the master, attempts to do now what he can, to destroy the souls of his disciples; and for that purpose he sent into the yard of the Abbey before their eyes seven naked young women, which there took hands together, play and dance a long time before them, to the end that, by this means, they might inflame their minds to sinful lust: which damnable sight the holy man beholding out of his cell, and fearing the danger which thereby might ensue to his younger monks, and considering that all this was done only for his persecution, he gave place to envy; and therefore, after he had for those abbeys and oratories which he had there built appointed governors, and left some under their charge, himself, in the company of a few monks, removed to another place.
And thus the man of God, on humility, gave place to the other's malice; but yet almighty God of justice severely punished [Florentius'] wickedness. For when the foresaid Priest, being in his chamber, understood of the departure of holy Benedict, and was very glad of that news, behold (the whole house besides continuing safe and sound) that chamber alone in which he was, fell down, and so killed him: which strange accident the holy man's disciple Maurus understanding, immediately sent him word, he being as yet scarce ten miles off, desiring him to return again, because the Priest that persecuted him was slain; which thing when Benedict heard, he was passing sorrowful, and lamented much: both because his enemy died in such sort, and also for that one of his monks rejoiced thereat; and therefore he gave him penance, for that, sending such news, he presumed to rejoice at his enemy's death."