It is narrated from Sayyiduna Jabalah bin Harithah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When you go to your bed, recite 'Qul ya ayyuha al-kafirun' (Say: O disbelievers) until you reach its end, for it is a declaration of freedom from shirk (associating partners with Allah)."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2182