Musnad Ahmad 26:362

'Affan narrated to us, Hammam narrated to us, 'Asim ibn Bahdalah narrated to us, from Abu al-Duha, from Masruq, from Ibn Mas'ud, from the Prophet, peace and blessings of Allah be upon him, that he said: "The two eyes commit adultery, and the two hands commit adultery, and the two feet commit adultery, and the private part commits adultery."