It is reported from Al-Hasan Al-Basrî – Allâh have mercy on him – that he said:

It used to be said: it is part of al-nifâq (hypocrisy) to be inwardly different from what you are on the outside, to say one thing and do another and to be different in how you enter and how you leave. And the root of al-nifâq is lying.

Abû Bakr Al-Kharâ`itî, Masâwî Al-Akhlâq wa Madhmûmihâ p62.