Qur'an 8:11

إِذْ يُغَشِّيكُمُ ٱلنُّعَاسَ أَمَنَةً مِّنْهُ وَيُنَزِّلُ عَلَيْكُم مِّنَ ٱلسَّمَآءِ مَآءً لِّيُطَهِّرَكُم بِهِۦ وَيُذْهِبَ عَنكُمْ رِجْزَ ٱلشَّيْطَـٰنِ وَلِيَرْبِطَ عَلَىٰ قُلُوبِكُمْ وَيُثَبِّتَ بِهِ ٱلْأَقْدَامَ

When He made the slumber fall upon you as a reassurance from him and sent down water from the sky upon you, that thereby He might purify you, and remove from you the fear of Satan, and make strong your hearts and firm (your) feet thereby.