Musannaf Ibn Abi Shayba 27:379

Muhammad ibn Bishr narrated to us, Mis'ar narrated to us, from Musa ibn Abi Kathir, from Mujahid, who said: Umar passed by the Messenger of Allah (peace and blessings of Allah be upon him) while he and Aisha were eating *hays* (a dish of dates, ghee, and dried yogurt). He invited him, so he placed his hand with their hands, and his hand touched the hand of Aisha. He said, "Oh! If he were obeyed regarding this and her companions, eyes would not have seen them." He said: And that was before the verse of the hijab. He said: Then the verse of the hijab was revealed.