Musnad Ahmad 3:129

'Abdullah narrated to us, Muhammad ibn Ishaq al-Musayyibi narrated to me, Anas ibn 'Iyad narrated to us, from Abu Mawdud, from Muhammad ibn Ka'b, from Aban ibn 'Uthman, from 'Uthman, that the Prophet, peace and blessings of Allah be upon him, said: "Whoever says: 'In the name of Allah, with whose name nothing on earth or in heaven can cause harm, and He is the All-Hearing, the All-Knowing' (Bismillahi alladhi la yadurru ma'a ismihi shay'un fi al-ardi wa la fi al-sama'i wa huwa al-sami'u al-'alim), three times, no sudden affliction will strike him until the evening. And whoever says it when he enters the evening, no sudden affliction will strike him until he enters the morning, if Allah wills."