Surah Al-Anfal — Ayah 11 (8:11)
إِذۡ يُغَشِّيكُمُ ٱلنُّعَاسَ أَمَنَةٗ مِّنۡهُ وَيُنَزِّلُ عَلَيۡكُم مِّنَ ٱلسَّمَآءِ مَآءٗ لِّيُطَهِّرَكُم بِهِۦ وَيُذۡهِبَ عَنكُمۡ رِجۡزَ ٱلشَّيۡطَٰنِ وَلِيَرۡبِطَ عَلَىٰ قُلُوبِكُمۡ وَيُثَبِّتَ بِهِ ٱلۡأَقۡدَامَ ١١
English translation (Saheeh International)
[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.
Brief commentary
And remember O believers when Allah made you fall asleep on that occasion, giving you a feeling of safety and peace from the fear you had of your enemy. He sent down rain from the sky on you, to purify you, and to remove the evil suggestions of Satan from you and to make your hearts strong, so you would be patient when you met the enemy in battle. It also made your feet firm, by making the sandy ground hard so that your feet would not sink and slip on it.