As-Salaam alaikum,
May I have the pleasure of sharing with you some of the wise and knowledgeable sayings of Imam Sahl al-Tustari (d. 283 A.H/893 C.E) as follows:--

(1) ''We have 6 principles: Holding fast to the Qur'an; taking the Sunnah as a guide;
eating what is licit; quitting from harm and avoiding sin; Repentance; Fulfillment
of obligations.''

(2) ''Among the manners of the most truthful and trustful Saints (al-Siddiqin) is that
they never swear by Allah, nor commit backbiting, nor does backbiting take place
around them, nor do they eat to satiation. If they promise, they are true to their
word, and they never speak in jest.''

(3) ''Allah does not open the heart of a servant if it still contains 3 things: loving to
remain [in the world], love of wealth, and concern about tomorrow.''

(4) ''When the servant abides in a specific sin, all his good deeds are admixed with
his egotism (hawa). His good deeds are not purified as long as he abides in a
single sin. He will not deliver himself from his egotism until he ousts from himself
all that he knows to be abhorred by Allah.''

SOURCE: 'Sahl al-Tustari (R.A), by G.F Haddad.