The Quran

إِذ يُغَشّيكُمُ النُّعاسَ أَمَنَةً مِنهُ وَيُنَزِّلُ عَلَيكُم مِنَ السَّماءِ ماءً لِيُطَهِّرَكُم بِهِ وَيُذهِبَ عَنكُم رِجزَ الشَّيطانِ وَلِيَربِطَ عَلىٰ قُلوبِكُم وَيُثَبِّتَ بِهِ الأَقدامَ

Muhammad Asad

[Remember how it was] when He caused inner calm to enfold you,¹ as an assurance from Him, and sent down upon you water from the skies, so that He might purify you thereby and free you from Satan's unclean whisperings² and strengthen your hearts and thus make firm your steps.

Le., before the battle of Badr. Regarding the interpretation of nu'as as "inner calm", see surah 3, note 112. Here it refers to the spiritual quiet and self-confidence of the believers in the face of overwhelming odds.
Lit., "take away from you the pollution of Satan". Immediately before the beginning of the battle, the Meccan army invested the wells of Badr, thus depriving the Muslims of water; and, under the influence of thirst, some of the latter fell prey to utter despair (here symbolized by "Satan's unclean whisperings") - when, suddenly, abundant rain fell and enabled them to satisfy their thirst (Tabari, on the authority of Ibn 'Abbds). '