1 Samuel 24:4

And again when the men who were with him counselled David to slay Saul, through his simple mind he refrained. That they should counsel him to slay his enemy arose from the cunning and craft of this world, for it is the custom of those who are filled with the cunning of this world to act craftily to remove obstacles from their path; but David in his simplicity and mercy refrained.

And David's servants said to him: Behold the day, etc. Christ's carnal disciples, still of a servile spirit, said to him when they saw the power of the crucified and the madness of those who crucified: Behold, the time is at hand, of which God the Father spoke to you through the mouth of his holy prophets from of old, that he would make all your enemies a footstool for your feet (Psalm 109). But they said this with their whole heart, although not in words, whomever of them desired the death of those who, releasing a thief, condemned the Savior to death, because it was proven by him who cut off the ear of the servant of the high priest, unwilling for the Lord to drink the cup which the Father gave. It was proven in those who sought fire from heaven to descend upon the impious, not knowing of what spirit they were, for the Son of Man did not come to destroy souls, but to save. But with the appropriate moderation of his piety, he did not completely kill the wicked, but withdrew from them, in no small part, the habit of the kingdom, so that even thus confounded, they might come to the recognition of their madness and correction.

When, therefore, he was alone and had removed his robe and laid it down somewhere beside him, the light from the mouth of the cave made him visible to those hidden within the darkness. All of David's companions wanted to rush upon the enemy and avenge themselves on the one who had come to kill them, since God had given the enemy into the hands of those who were being pursued for slaughter. But David forbade them to attack, considering an assault against their king unlawful. He drew his own sword from its sheath and imperceptibly stood behind Saul. There was no witness to his undertaking against Saul, for the darkness in the cave concealed his appearance and prevented scrutiny of what was happening. When, then, he could have driven his whole sword through Saul's heart from behind with one blow, he neither touched his body nor was he about to. But he secretly cut off the end of his robe with his sword, so that the garment might be a witness later of his clemency toward Saul and prove the power that he had had to strike a blow against Saul's body by means of the cut at its end.By this it became obvious that David had been trained in forbearance. When he held the bare sword in his palm, and the body of his enemy lay under his hand, he had the power to kill him, but he conquered his anger with reason, and his power to strike the blow with the fear of God. Not only did he become superior to his own anger, but he also restrained his shield bearer who was eager to murder Saul, addressing him with that saying famous in song, "Destroy not the anointed of the Lord."