Judges 6:36-40 (Eve of the Theophany)
Then Gideon said to God, "If thou wilt deliver Israel by my hand, as thou hast said, behold, I am laying a fleece of wool on the threshing floor; if there is dew on the fleece alone, and it is dry on all the ground, then I shall know that thou wilt deliver Israel by my hand, as thou hast said." And it was so. When he rose early next morning and squeezed the fleece, he wrung enough dew from the fleece to fill a bowl with water. Then Gideon said to God, "Let not thy anger burn against me, let me speak but this once; pray, let me make trial only this once with the fleece; pray, let it be dry only on the fleece, and on all the ground let there be dew." And God did so that night; for it was dry on the fleece only, and on all the ground there was dew.