Musnad Ahmad 30:2559

Muhammad ibn Ubayd narrated to us, from Yazid ibn Kaysan, from Abu Hazim, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to his uncle: "Say: 'There is no god but Allah,' I will testify for you with it before Allah on the Day of Resurrection." He said: "Were it not that Quraysh would reproach me, I would have gladdened your eye with it." He said: Then Allah, the Almighty and Majestic, revealed: {Indeed, you do not guide whom you like, but Allah guides whom He wills. And He is most knowing of the [rightly] guided} [Al-Qasas: 56].