Musnad Ahmad 30:2491

Yahya narrated to us, from Shu'bah, who said: Al-'Ala' ibn 'Abd al-Rahman narrated to us, from his father, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said—meaning—Allah (Mighty and Majestic is He) said: "I am the best of partners. Whoever performs a deed for Me in which he associates someone else with Me, then I am free of it, and it is for the one whom he associated [with Me]."