Musnad Ahmad 27:1379

Ya'la ibn 'Ubayd narrated to us, al-A'mash narrated to us, from Ibrahim, from Abu al-Sha'tha', who said: It was said to Ibn 'Umar: "We enter upon our leaders and we say a statement, but when we exit, we say other than it." He said: "We used to consider this, during the time of the Messenger of Allah (peace and blessings of Allah be upon him), to be hypocrisy."