John Cassian, Conferences I–X V.5: How our Lord alone was tempted without sin

And so our Lord Jesus Christ, though declared by the Apostle’s word to have been tempted in all points like as we are, is yet said to have been “without sin,” i.e., without the infection of this appetite, as He knew nothing of incitements of carnal lust, with which we are sure to be troubled even against our will and without our knowledge; for the archangel thus describes the manner of His conception: “The Holy Ghost shall come upon thee and the power of the Most High shall overshadow thee: therefore that which shall be born of thee shall be called holy, the Son of God.”