Yahya ibn Adam narrated to us, Sufyan narrated to us, from Abu Ishaq, from Farwah ibn Nawfal al-Ashja'i, that the Messenger of Allah, peace and blessings be upon him, said to a man: "Recite at your bedtime: 'Say: O disbelievers' (Qul ya ayyuhal kafirun), for indeed it is a declaration of innocence from shirk (associating partners with Allah)."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 24009/53