Musnad Ahmad 30:882

Rawh narrated to us, Shu'bah narrated to us, al-'Ala' ibn 'Abd al-Rahman ibn Ya'qub narrated to us, I heard my father narrating from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said to me: "Allah, the Almighty and Majestic, said: 'I am the best of partners. Whoever performs a deed for Me, but associates someone else with Me in it, then I am free of it, and it is for the one whom he associated [with Me].'"