Midrash sur La Genèse 9:15

When Pharaoh shall speak unto you, saying: “Show a wonder for you” (Exod. 7:9). He will be making a reasonable request to you. You find in the case of Noah, that though He said to him, after He saved him from the flood, Neither shall there be anymore a flood (Gen. 9:11), Noah demanded a sign, and God assured him: I have set my bow in the cloud (ibid., v. 13). Similarly, when Hezekiah was sick, the Holy One, blessed be He, sent Isaiah to him and he said: Thus saith the Lord, the God of David, thy father: “I have heard thy prayer, I have seen thy tears; behold, I will heal thee; on the third day thou shalt go up unto the house of the Lord” (II Kings 20:5). But he replied: What shall be the sign? (ibid., v. 8), and He answered: This shall be the sign unto thee from the Lord, that the Lord will do the thing that He hath spoken: shall the shadow go forward ten degrees, or go back ten degrees? (ibid., v. 9). Likewise, Joshua, the high priest, was told: Hear now, O Joshua the high priest, … for they are men that are a sign (Zech. 3:8). Since the righteous demanded signs, how much more did the wicked Pharaoh (have the right to do so). Hence, when Pharaoh says unto you: Show a wonder for you (he will be making a reasonable request).

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"And I will remember my covenant." When there is a cloud over the land, I will remember my covenant that I sealed with you, and I will show you a the rainbow in the cloud, and you will know that I remember my covenant that a flood will not destroy all flesh."