Musnad Ahmad 28:93

Abu Abd al-Rahman narrated to us, Haywah narrated to us, Abu Hani’ informed me that he heard Abu Abd al-Rahman al-Hubuli, that he heard Abdullah ibn Amr, that he heard the Messenger of Allah (peace and blessings of Allah be upon him) saying: "Indeed, the hearts of all the children of Adam are between two fingers from the fingers of the Most Merciful, Mighty and Majestic is He, as one heart; He directs it however He wills." Then the Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, Director of the hearts, direct our hearts toward Your obedience."