It is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him, that indeed the Messenger of Allah, peace and blessings be upon him, said: "It is not possible for a two-faced person to be trustworthy with Allah."
Explanation: By a two-faced person is meant such an individual who adopts duplicity; when he goes to one group, he makes them believe that he is their well-wisher and an enemy of their opponents, but when he goes to the opponents, he gives the same impression there—that he is their well-wisher and an enemy of their opponents. Such a person has no personal integrity; he merely aligns himself with whichever side benefits him in this world. How can such a person be considered trustworthy in the sight of Allah Ta‘ala? Indeed, he is the worst of people, as mentioned in the noble hadith. See also hadith number 606.