Musnad Abu Ya'la al-Mawsili 115:283

Musa ibn Abd al-Rahman al-Sulami narrated to us, Umar ibn Sa'id al-Abbah narrated to us, from Sa'id, from Qatadah, from Anas, 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.