Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) once mentioned:
The principle in regard to one’s Islamic beliefs is that one should make a concerted effort to strengthen his Islamic beliefs, and he should not entertain stray thoughts, thereby allowing them to affect his Islamic beliefs. Thereafter (i.e. after believing in all the tenets of faith correctly), one should still have the concern and worry in his heart as to whether he has acquired the desired level of yaqeen (conviction) in his beliefs or not.
Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) then said, “The statement of Hazrat Ibnu Abi Mulaikah (rahimahullah) recorded in Saheeh Bukhaari shareef refers to this very same level of imaan and yaqeen when he said:
لقيت ثلاثين من أصحاب النبي صلى الله عليه وسلم كلهم يخشى على نفسه النفاق
I had met thirty of the companions of Rasulullah (sallallahu ‘alaihi wasallam) (i.e. the Sahaabah [radhiyallahu ‘anhum]), and each one of them feared hypocrisy over himself.
(In other words, each Sahaabi feared that the level of his imaan has not reached the highest levels of perfection, and therefore he expressed concern of nifaaq.)
Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) thereafter mentioned:
Strengthening one’s imaan and conviction is also necessary so that whenever one hears the words of Allah Ta‘ala and Rasulullah (sallallahu ‘alaihi wasallam), then one’s heart will immediately receive these words with great honour, respect and reverence.
In this case (when one receives the word of Allah Ta‘ala and Rasulullah (sallallahu ‘alaihi wasallam) with firm conviction), then it will be easy for one to practise upon the commandments of Allah Ta‘ala and Rasulullah (sallallahu ‘alaihi wasallam) (as one’s imaan will motivate him to do so), and there will be life in one’s actions as well (due to one’s imaani level being high).
(Malfoozaat Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) pg. 84-85)