John Calvin Commentary Exodus 8:27

"We will go three days` journey into the wilderness, and sacrifice to Jehovah our God, as he shall command us." — Exodus 8:27 (ASV)

We will go three days’ journey. This is the conclusion that no change must be made in God’s command, but that His injunction must be obeyed simply, and without exception. Nor is little praise due to the firmness of Moses, who so boldly and unreservedly rejected the pretended moderation of the tyrant, because it would have somewhat interfered with the will of God. He therefore declares that the Israelites would do only as God had prescribed.