Musnad Abu Ya'la al-Mawsili 117:62

Hawthara ibn Ashras narrated to us, Mubarak ibn Fadala narrated to us, from Thabit al-Bunani, from Anas ibn Malik, that a man said: "O Messenger of Allah, I love 'Say, He is Allah, [who is] One'." He said: "Your love for it will cause you to enter Paradise."