Musannaf Ibn Abi Shayba 21:84

Ghundar narrated to us, from Shu'bah, from Mansur, from Mujahid, from Abdullah ibn Damrah, from Ka'b al-Ahbar, who said: "When a person leaves his house and says, 'In the name of Allah, I rely upon Allah, and there is no power except by Allah' (Bismillahi tawakkaltu 'ala Allahi wa la quwwata illa billah), the devils convey to one another, saying: 'This is a servant who has been guided, protected, and sufficed; you have no way to reach him.' So they disperse away from him."