Musnad Ahmad 30:2208

Affan narrated to us, he said: Abd al-Rahman ibn Ibrahim narrated to me, he 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: "The two eyes commit adultery, and the tongue commits adultery, and the two hands commit adultery, and the two feet commit adultery; and the private part confirms that or denies it."