Imam Sufyaan ath-Thawri (rahimahullah) wrote in a letter of advice to one of his Brothers in Islam:
“….The most wise of the wise ones, is he who enters Paradise because of a sin he perpetrated: He places his sin before his eyes, continuing to be constantly afraid for himself on account of that sin until he departs from this world and enters Paradise.
And the most foolish of the foolish ones is he who enters the Hellfire on account of a single good deed he performed: He places it before his eyes, constantly remembering it and hoping to be rewarded for it, and in the meanwhile, he takes his sins lightly; and he continues to remain upon that condition until he parts from this world and enters the Hellfire.
My Brother, be wise: be constantly afraid for yourself on account of your past mistakes, since you do not know whether or not your Lord will punish you for them. And you do not know what impact your sins will have on the remainder of your life.
Remember, that Ibraheem (alayhi salam) despite the fact that he was the Khaleel ar-Rahmaan (this was a position of high ranking with his Lord), feared for himself and asked his Lord:“O my Lord…keep me and my sons away from worshipping idols.” (Qur’an 14: 35)
“And Yousuf (alayhi salam) said:“My Lord…cause me to die as a Muslim (the one submitting to Your Will), and join me with the righteous.” (Qur’an, 12: 101)
And Moosa (alayhi salam) said: “My Lord! For that which You have favored me, I will never more be a helper for the Mujrimun (criminals, disobedient to Allah, polytheists, sinners, etc)!” (Qur’an, 28: 17)
And Shu’aib (alayhi salam) said: “And it is not for us to return to it unless Allah, our Lord, shall will.” (Qur’an 7: 89)
All of these Prophets of Allah feared for themselves (so imagine the degree to which we should fear for ourselves).
And remember that a Muslim is a person from whose tongue and hand other Muslims are safe.”