Musnad Ahmad 31:832

Hashim narrated to us, from Shu'bah, from Qatadah, from Ibn Abi 'Utbah, from Abu Sa'id, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) was more bashful than a virgin in her private quarters. And if he disliked something, we would recognize it in his face."