Rashi, on Gen 15:12

“And when the sun was setting, a deep sleep fell upon Abram, and a great and darksome horror seized upon him.”

“'והנה אימה וגו AND, LO, AN HORROR etc. — This is symbolic of the woes and the gloom of the Jews in Exile (Genesis Rabbah 44:17).”

Imported from an open dataset — not yet checked against the printed edition.