Midrash su Salmi 132:18

Abraham arose and prayed before the Holy One, blessed be He, that his children should not be enslaved by these four kingdoms. A deep sleep fell upon him, and he slept, as it is said, "A deep sleep fell upon Abram" (Gen. 15:12). Does then a man lie down and sleep, and yet be able to pray? But this teaches thee that Abraham was lying down and sleeping because of the intensity of his prayer that his children might enslave || these four kingdoms, as it is said, "And, lo, an horror of great darkness fell upon him" (ibid.). "Horror" refers to the kingdom of Edom, as it is written, "And behold a fourth beast, terrible and powerful, and strong exceedingly" (Dan. 7:7). "Darkness" is the kingdom of those who darken the eyes of Israel (by preventing the observance of) all the precepts which are in the Torah. "Great" (Gen. 15:12) refers to the kingdom of Media and Persia, which was great (enough to be able to afford) to sell Israel for nought. "Fell" (ibid.) refers to the kingdom of Babylon, because in their hand fell the crown of Israel, as it is said, "Babylon is fallen, is fallen" (Isa. 21:9). "Upon him" (Gen. 15:12) refers to the Ishmaelites, upon whom the Son of David will flourish, as it is said, "His enemies will I clothe with shame: but upon him shall his crown flourish" (Ps. 132:18).