John Gill

And behold one of them which were with Jesus,.... Either one of the three that Jesus took with him whilst he was in his agony, leaving the other eight at some distance; or of the eleven, who might now be all with him: however, it is certain, Peter is the person meant; for though he is not named here, nor by Mark, nor Luke, he is by John, Joh 18:10; whose Gospel being wrote last, and many years after the rest, there was no danger like to accrue, by telling who it was that did the following action: he being now thoroughly awaked with the rest, by what Christ had said to him; and more so by the surprise of the multitude of armed men about him; and remembering his solemn protestations of abiding by his master; and seeing him just now ready to be seized, and carried away; without knowing his master's mind, or waiting his answer to the question the other disciples put, stretched out his hand, and drew his sword, and struck a servant of the high priest's, and smote off his ear. It seems he had a sword by his side, upon what account is not certain; this he drew, and struck at a servant of the high priest's, who might show great malignity against Christ, and was foremost, and most busy in apprehending him. The blow was levelled at his head, and with an intention, no doubt, to have, cleaved him down, but sloping on one side took off his ear. The servant's name was Malchus, as John says; and it was his right ear that was cut off, as both he and Luke relate, Joh 18:10.