Question: What are the types of souls? And What is the way to purify it and its path as Allah, the Exalted said: Indeed he succeeds who purifies his oneself [91:9]?
Answer: The types of souls mentioned in the Noble Quran are three: the soul that commands evil ( أمارة بالسوء), the self-reproaching soul (النفس اللوامة), and the pious soul (النفس المطمئنة). The soul that orders evil is the one who commands its owner to its prohibited desires and following falsehood. As for the self-reproaching soul: it makes its owner feel guilty for what passed it of good and makes him remorseful for it. As for the pious soul: it is the one that feels tranquil with its Lord and His obedience, commands, and remembrance. It is not feel settled/tranquil with other than it. Allamah Ibn Qayyim rahimahullah said: It being called pious (مطمئنة ) is a description of praise for it. And (أمارة بالسوء) is a blameworthy description for it and (النفس اللوامة) is a description to praise and blameworthiness in accordance to what the soul feels guilty about. The way to purify the soul is by holding fast to the obedience of Allah, the Exalted, preventing it from His disobedience, and prohibited desires”.
[Muntaqa min Fatawa Shaikh Salih al-Fawzan (2/134)]
Faisal Ibn Abdul Qaadir Ibn Hassan