Musnad Ahmad 32:1752

'Affan narrated to us, 'Abd al-Wahid narrated to us, Sulayman ibn Mihran narrated to us, from Abu Sufyan, from Anas ibn Malik, who said: The Messenger of Allah, peace and blessings of Allah be upon him, used to frequently say: "O Turner of the hearts, make my heart firm upon Your religion." His companions and his family said to him: O Messenger of Allah, do you fear for us, while we have believed in you and in what you have brought? He said: "Indeed, the hearts are in the hand of Allah; He turns them."