Allah's Messenger (peace be upon him) said, "Fasting and the Qur'an intercede for a man. Fasting says, 'O my Lord, I have kept him away from his food and his passions by day, so accept my intercession for him.' The Qur'an says, 'I have kept him away from sleep by night, so accept my intercession for him.' Then their intercession is accepted."
Bayhaqi transmitted it in Shu'ab al-Iman.