Unbelief stands on four supports: hankering after whims, mutual quarrelling, deviation from the truth, and dissension. So, whoever hankers after whims does not incline towards right: whoever quarrels much on account of ignorance remains permanently blinded from the right; whoever deviates from truth, for him good becomes evil and evil becomes good and he remains intoxicated with misguidance; and whoever makes a breach (with Allah and His Messenger), his path becomes difficult, his affairs become complicated and his way of escape becomes narrow. Doubt has also four aspects: unreasonableness, fear, wavering and undue submission to every thing. So, he who adopts unreasonableness as his way, for him there is no dawn after the night; he who is afraid of what befalls him has to run on his heels; he who wavers in doubt Satans trample him under their feet and he who submits to the destruction of this and tile next world succumbs to it.
— ALI IBN ABI TALIB