Judges 6:37

behold, I will put a fleece of wool in the floor, out in the open on the ground; and if the dew be on the fleece only, and if it be dry upon all the earth beside, then shall I know that Thou wilt save Israel by mine hand, as Thou hast said. He had such a humble opinion of himself and his influence that he felt the need of such a sign to establish his courage.