Al-Anfal 8:11

Ith yughashsheekumu annuAAasaamanatan minhu wayunazzilu AAalaykum mina assama-imaan liyutahhirakum bihi wayuthhiba AAankumrijza ashshaytani waliyarbita AAalaquloobikum wayuthabbita bihi al-aqdam

[Remember] when He overwhelmed you with drowsiness [giving] security from Him and sent down upon you from the sky, rain by which to purify you and remove from you the evil [suggestions] of Satan and to make steadfast your hearts and plant firmly thereby your feet.

When He covered you with drowsiness, as tranquility (descending) from Him and sent down upon you water from the heavens, so that He might purify you with it, and remove from you the impurity of Satan, and so that He might strengthen your hearts and make (your) feet firm therewith.