By believing in Allah, your heart is reassured

The only way to obtain the tranquility of the heart and self-assurance lies in believing in God, in the Qur’an, and to follow the Prophet Muhammad, may God bless him and grant him peace

Allah said ( interpretation of the meaning ) : { Those who have believed and whose hearts are assured by the remembrance of Allah . Unquestionably, by the remembrance of Allah hearts are assured." } Quran ( 13 : 28 )