Certainty-and that is firm, established and unshakeable faith in which there is no doubt and (the faith) which does not hesitate, suspect or doubt in the five fundamentals that Allaah, the Exalted, has mentioned in His saying:

"It is not Al-Birr (piety, righteousness and obedience to Allaah) that you turn your faces towards east and (or) west (in prayers); but Al-Birr is (the quality of) the one who believes in Allaah, the Last Day, the Angels, the Book and the Prophets. [Soorah al-Baqarah (2):177].

The Messenger (sallallahu alaihiwasallam) combined them all in the hadeeth of Umar RA in his saying about eemaan, "That you believe in Allaah, His Angels, His Books, His Messengers and the Final Day.." [reported by al-Bukharee (1/20) and Muslim (1/37) from Umar ibn al-Khattaab].

Certainty is that a (person’s) faith in these fundamentals is strengthened until they become visible to the heart, evident to it, their relationship to keen insight (baseerah) being like the relation of the sun and the moon to the sight (i.e., clearly visible).

~ IBN JOWZY ~