Musannaf Ibn Abi Shayba 21:190

Al-Fadl ibn Dukayn narrated to us, Zuhayr narrated to us, from Abu Ishaq, from Asim, from Ali, who said: "When you take to your bed, say: 'In the name of Allah, and in the way of Allah, and upon the religion of the Messenger of Allah, may Allah bless him and grant him peace.'"