Musnad Ahmad 31:755

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Qatadah, that he heard a freed slave of Anas ibn Malik narrating from Abu Sa'id al-Khudri, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) was more bashful than a virgin in her private chamber. And if he disliked something, it would be recognized in his face."