[...from] "When He covered you with drowsiness [as] a security from Him" to His saying: "I will cast terror into the hearts of those who disbelieved."

The interpretation of al-Kalbi: He said:

It has reached us that the polytheists preceded the Messenger of Allah to the water of Badr. The Messenger of Allah arrived and encamped opposite them, with the valley between him and them, and he encamped on ground without water. Then Satan cast a grievous matter into the hearts of the believers, saying: "You claim that you are the servants of Allah and upon the religion of Allah, yet the polytheists have overcome you regarding the water, while you are praying in a state of ritual impurity (hadath) and major impurity (janabah)." So Allah willed to remove the filth of Satan from their hearts, and He covered the believers with drowsiness as a security from Him, and He sent down water from the sky to purify them thereby from ritual impurities and major impurity, and to remove from them the filth of Satan—that which he had cast into their hearts—and to strengthen their hearts and to make firm the feet therewith. The bottom of the valley contained sand in which feet would sink; when the valley was rained upon, the sand hardened, and the men walked upon it. The Messenger of Allah then fashioned basins in the valley, from which the Muslims drank and drew water, then they aligned for battle. And your Lord revealed to the angels: "I am with you, so strengthen those who have believed. I will cast terror into the hearts of those who disbelieved."

"So strike [them] above the necks." Al-Hasan said: Meaning: Strike the necks, (and strike...