For perfecting Imaan, there are certain requisites. These are outlined in the Quraan where Allah Ta‘ala explains three requisites:
1. Nabi’s (sallallahu ‘alaihi wasallam) decision is final in all matters.
2. There should not be even the slightest reservation within one’s heart and mind regarding the decision of Rasulullah (Sallallahu Alaihi Wasallam).
3.One should wholeheartedly accept the decision of Rasulullah (Sallallahu Alaihi Wasallam) irrespective of the circumstance and situation.
Therefore, for the preservation of our Imaan, one simple method would be to make the following du‘aa after every salaah:
اَللَّهُمَّ تَوَفَّنِى مُسْلِمَا وَّاَلْحِقْنِى بِالصَّالِحِين
O Allah! Make me die as a Muslim and join me in the ranks of the pious.