Musnad Ahmad 25:1139

Yahya ibn Adam narrated to us, Ibn al-Mubarak narrated to us, from Ma’mar, from Yahya ibn Abi Kathir, from ‘Ikrimah, from Ibn ‘Abbas, that the Messenger of Allah (peace and blessings of Allah be upon him) said to Ma’iz when he said, "I have committed adultery": "Perhaps you squeezed, or kissed, or looked at her?" He said: "It is as if he feared that he did not know what adultery was."