The Book of Imaan: The Basis, reality and invalidation of Emaan 

Accordingly, the most noble knowledge a man can learn and teach to others is the basis of belief (emaan) and its requirements. The best precautionary measures he can protect himself with is the knowledge of the characteristics of disbelief (Kufr), its causes and exigencies. If man has insight into these two important things, he will know the way of his happiness and follow it, and avoid the way of his misery.

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