Asim bin Muhammad reports from his father that a man said to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both): We go in to the ruler and say things to him other than what we say in his absence. He said: We regarded this as hypocrisy.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16661
Abu Hurayrah (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "The worst of people is the two-faced one, who comes to these with one face and to those with another face."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16662