‘And Moses said, “Eat that today. For today is a sabbath in honour of Yahweh. Today you will not find it in the surrounding area (field, countryside). Six days you will gather it, but on the seventh day is the Sabbath, in it there will be none.” And so it was that on the seventh day some of the people went out in order to gather, and they found none.'
No Manna could be gathered on the Sabbath because there was none available. It was ‘a Sabbath unto Yahweh', a day of quietness for the purpose of honouring and worshipping Him. Yet inevitably some went out to see what they could find. But they found none as they had been told. There can be no explanation for this except the hand of Yahweh. It is a reminder that God often controls the natural, as He had done in Egypt, rather than doing spectacular miracles.