I think it worthy observation, that the Lord who hath all hearts at his disposal, not only made a difference between the believing Israelite and the unbelieving Egyptian; but between one Egyptian and another. Some of the cattle of Egypt would be needed for the chariots and horsemen in the pursuit of Israel, which by and by was to take place. Hence the Lord inclined some of the Egyptians to take home their cattle to their houses.
Related Commentaries of Exodus 9:19
Exodus 9:19-21
19 Send therefore now, and gather thy cattle, and all that thou hast in the field; for upon every man and beast which shall be found in the field, and shall not be brought home, the hail shall come down upon them, and they shall die.
20 He that feared the word of the LORD among the servants of Pharaoh made his servants and his cattle flee into the houses:
21 And he that regardeda not the word of the LORD left his servants and his cattle in the field.