To be blessed with a large store of knowledge, a mind that contemplates, a good understanding, and an intellect that delves beneath the surface for reasons and motives --- these are all factors that contribute to giving one peace of mind.
(It is only those who have knowledge among His slaves that fear , Allah)
(Qur'an 35: 28)
(Nay, they deny that; the knowledge whereof they could not compass...)
(Qur'an 10: 39)
A scholar usually has an open mind and is at peace. A thinker from the west said:
"l keep a large file in the drawer of my desk, and on it is written, 'Foolish things I have done.' I write in it all of the follies and errors that I perpetrate during the course of a day; I do this to know my faults in order to rid myself of them."
The earlier Muslim scholars preceded him in this endeavor. They would meticulously take an account of their deeds.
(And I swear by the self-reproaching person [a believer].)
(Qur'an 75: 2)
Al-Hasan al-Basri said:
"The Muslim takes account of himself with more rigor than does a businessman with his partner."
Ar-Rabee' ibn Khuthaym would write everything that he said from one Friday to the next. If he found that he had spoken well and truthfully, he praised Allah. And if he found error in his speech, he repented to Allah. A righteous man from the early centuries of Islam said,
"I committed a particular sin forty years ago, a sin that still bothers me today. I continue to ask Allah to forgive me for it."
(And those who give that [their charity] which they give [and also do other good deeds] with their hearts full of fear [whether their alms and charities, etc., have been accepted or not]...) (Quran 23: 60)