Musannaf Ibn Abi Shayba 23:11

Zayd ibn al-Hubab narrated to us, from Ali ibn Mas'adah, who said: Qatadah narrated to us, who said: Anas ibn Malik narrated to us, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Islam is public, and faith is in the heart." Then he pointed with his hand to his chest and said: "Piety is here, piety is here."