Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

The king appointed the following day, probably because he hardly thought it possible for so great a work to be performed at once. Moses promised that it should be so: "According to thy word (sc., let it be), that thou mayest know that there is not (a God) like Jehovah our God." He then went out and cried, i.e., called aloud and earnestly, to Jehovah concerning the matter (דּבר על) of the frogs, which he had set, i.e., prepared, for Pharaoh (שׂוּם as in Gen 45:7). In consequence of his intercession God took the plague away. The frogs died off (מן מוּת, to die away out of, from), out of the houses, and palaces, and fields, and were gathered together by bushels (חמרים from חמר, the omer, the largest measure used by the Hebrews), so that the land stank with the odour of their putrefaction. Though Jehovah had thus manifested Himself as the Almighty God and Lord of the creation, Pharaoh did not keep his promise; but when he saw that there was breathing-time (רוחה, ἀνάψυξις, relief from an overpowering pressure), literally, as soon as he "got air," he hardened his heart, so that he did not hearken to Moses and Aaron (והכבּד inf. abs. as in Gen 41:43).