Tractate Makhshirin - Chapter 3 - Mishnah 4 מכשירין פרק ג׳ משנה ד׳

If one sprinkled [the floor of] his house [with water] and put wheat therein and it became moist: If [the moisture came] from the water, it comes under the law of ‘if water be put’; But if [the moisture came] from the stones [on the floor], it does not come under the law of ‘if water be put’. If one washed his garment in a tub and put wheat therein and it became moist: If [the moisture came] from the water, it comes under the law of ‘if water be put’; But if [the moisture came] of itself, it does not come under the law of ‘if water be put’. If one put [produce] in sand for it to become moist, this comes under the law of ‘if water be put’. It happened with the men of Mahoz that they used to moisten [their produce] with sand, and the sages said to them: if you have always acted in this manner, you have never prepared your food in purity.