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.
Hadith Referenceمشكوة المصابيح / كتاب فضائل القرآن / 2161
Hadith Gradingالألبانی:لم تتمّ دراسته | زبیر علی زئی:حسن
Hadith Takhrij´تحقيق و تخريج: محدث العصر حافظ زبير على زئي رحمه الله` «حسن، رواه الترمذي (3403) و أبو داود (5055) و الدارمي (459/2 ح 3430)»