Matthew 4:2

And when he had fasted forty days and forty nights--Luke says "When they were quite ended" (Luk 4:2). he was afterward an hungered--evidently implying that the sensation of hunger was unfelt during all the forty days; coming on only at their close. So it was apparently with Moses (Exo 34:28) and Elijah (Kg1 19:8) for the same period. A supernatural power of endurance was of course imparted to the body, but this probably operated through a natural law--the absorption of the Redeemer's Spirit in the dread conflict with the tempter. (See on Act 9:9). Had we only this Gospel, we should suppose the temptation did not begin till after this. But it is clear, from Mark's statement, that "He was in the wilderness forty days tempted of Satan" (Mar 1:13), and Luke's, "being forty days tempted of the devil" (Luk 4:2), that there was a forty days' temptation before the three specific temptations afterwards recorded. And this is what we have called the First Stage. What the precise nature and object of the forty days' temptation were is not recorded. But two things seem plain enough. First, the tempter had utterly failed of his object, else it had not been renewed; and the terms in which he opens his second attack imply as much.

— Jamieson-Fausset-Brown Commentary (public domain)