Musnad Abu Ya'la al-Mawsili 3:179

Al-Hasan ibn Hammad al-Kufi narrated to us, Muhammad ibn al-Hasan ibn Abi Yazid al-Hamdani narrated to us, from Ja'far ibn Muhammad, from his father, from his grandfather, from Ali, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Supplication is the weapon of the believer, the pillar of the religion, and the light of the heavens and the earth."