Tafsir of Ash-Shams 91:10

Indeed he succeeds who purifies it. And indeed he fails who Dassaha. This could mean that whoever purifies himself by obedience to Allah, then he will be successful. This is as Qatadah said, "He cleanses it from the lowly and despicable characteristics.'' Similar to this has been reported from Mujahid, `Ikrimah and Sa`id bin Jubayr

وقد خاب من دسها

And indeed he fails who Dassaha. meaning, to conceal it. This means that he makes it dull, and he disregards it by neglecting to allow it to receive guidance. He treats it in this manner until he performs acts of disobedience and he abandons obedience of Allah. It also could mean that he is indeed successful whose soul Allah purifies, and he has failed whose soul Allah corrupts. This is like what was reported by Al-`Awfi and `Ali bin Abi Talhah from Ibn `Abbas. At-Tabarani recorded that Ibn `Abbas said, "The Messenger of Allah used to stop whenever he recited this Ayah,

ونفس وما سواها

فٲلهمها فجورها وتقواها

By Nafs, and Ma Sawwaha (Who apportioned it). Then He showed it its Fujur and its Taqwa. Then he would say,

اللهم آت نفسي تقواها أنت وليها وموﻻها وخير من زكاها

O Allah! Give my soul its good. You are its Guardian and Master, and the best to purify it.'' Another Hadith Imam Ahmad recorded that Zayd bin Arqam said that the Messenger of Allah said,

اللهم إني أعوذ بك من العجز والكسل والهرم والجبن والبخل وعذاب القبر

اللهم آت نفسي تقواها وزكها أنت خير من زكاها أنت وليها وموﻻها

اللهم إني أعوذ بك من قلب ﻻ يخشع ومن نفس ﻻ تشبع وعلم ﻻ ينفع ودعوة ﻻ يستجاب لها

O Allah! Verily, I seek refuge with You from weakness, laziness, senility (of old age), cowardliness, stinginess and the torment of the grave. O Allah! Give my soul its good and purify it, for You are the best to purify it. You are its Guardian and Master. O Allah! Verily, I seek refuge with You from a heart that is not humble, a soul that is not satisfied, knowledge that does not benefit and a supplication that is not answered. Zayd then said, "The Messenger of Allah used to teach us these (words) and we now teach them to you.'' Muslim also recorded this Hadith