Charles Spurgeon Commentary Exodus 16:19-22

"And Moses said unto them, Let no man leave of it till the morning. Notwithstanding they hearkened not unto Moses; but some of them left of it until the morning, and it bred worms, and became foul: and Moses was wroth with them. And they gathered it morning by morning, every man according to his eating: and when the sun waxed hot, it melted. And it came to pass, that on the sixth day they gathered twice as much bread, two omers for each one: and all the rulers of the congregation came and told Moses." — Exodus 16:19-22 (ASV)

He had told them that it would be so, but they evidently did not accept the message that he had delivered to them as the very Word of Jehovah their God; so that, when it was fulfilled, it struck them with wonder, and they "came and told Moses."