Musnad Ahmad 432:0

It was narrated from Khalid ibn al-Walid that he said: "I came to the Messenger of Allah (ﷺ) and said: 'O Messenger of Allah, I am a man of war, and I have been given a share of it. So teach me a supplication that I may say.' He said: 'Say: "O Allah, I seek refuge in You from the evil of what I encounter in this war, and from the evil of what is in it, and from the evil of what is behind it, and from the evil of what I am upon, and from the evil of what I am heading towards."'"