Musnad Abu Ya'la al-Mawsili 160:30

Hadbata narrated to us, Hammad bin Salamah narrated to us, from Thabit, from Abu Rafi’, from Abu Hurairah, from the Prophet (peace be upon him), who said: "The two eyes commit adultery, the two hands commit adultery, and the two feet commit adultery; and the private part confirms that or denies it."