Prayer (Kitab Al-Salat): Detailed Injunctions about Witr
Dawud :: Book 8 : Hadith 1532
Narrated AbuMusa al-Ash'ari:
When the Prophet (peace_be_upon_him) feared a (group of) people, he would say: "O Allah, we make Thee our shield against them, and take refuge in Thee from their evils."