Musnad Abu Ya'la al-Mawsili 108:45

Abu al-Rabi' narrated to us, Salam—meaning Ibn Sulaym—narrated to us, from Muhammad ibn Abi Humayd, from Muhammad ibn al-Munkadir, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Shall I not guide you to that which will save you from your enemy and increase your provisions? Call upon Allah in your night and your day, for supplication is the weapon of the believer."