Mishkat al-Masabih 8 The Excellent Qualities of the Qur’an كتاب فضائل القرآن 51

وَعَنْ فَرْوَةَ بْنِ نَوْفَلٍ عَنْ أَبِيهِ: أَنَّهُ قَالَ: يَا رَسُولَ اللَّهِ عَلِّمْنِي شَيْئًا أَقُولُهُ إِذَا أَوَيْتُ إِلَى فِرَاشِي. فَقَالَ: «اقْرَأْ (قُلْ يَا أَيُّهَا الْكَافِرُونَ) فَإِنَّهَا بَرَاءَةٌ مِنَ الشِّرْكِ» . رَوَاهُ التِّرْمِذِيّ وَأَبُو دَاوُد والدارمي

Farwa b. Naufal quoted his father as saying that he had asked God’s messenger to teach him something to say when he went to bed, and was told to recite, “Say, O infidels”, for it is a declaration of freedom from polytheism. Tirmidhī, Abū Dāwūd and Dārimī transmitted it.