Musnad Abu Ya'la al-Mawsili 110:178

Hannad ibn al-Sari narrated to us, Yunus ibn Bukayr narrated to us, he said: Matar ibn Maymun al-Muharibi narrated to me, he said: Ikrimah narrated to me, from Ibn Abbas, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent a man from his companions to a man from the Jews and ordered him to kill him. He said: "O Messenger of Allah, I cannot do that unless you give me permission [to use deception]." The Messenger of Allah (may Allah bless him and grant him peace) said: "War is deception, so do what you wish."