On one occasion, a certain person enquired from Hazrat Moulana Ashraf Ali Thanwi (rahmatullahi ‘alaih) regarding the remedy and treatment for bad-gumaani (entertaining evil thoughts about people without any proof). In reply, Hazrat Thanwi (rahmatullahi ‘alaih) mentioned the following:
When an evil thought enters the heart regarding any person, then one should immediately sit in seclusion and think to himself, “Allah Ta‘ala has prohibited us from entertaining evil thoughts about people. Hence, it is a sin for me to entertain such evil thoughts regarding this person, and by me committing this serious sin, there is the fear of me being severely punished in the Hereafter.”
One should thereafter address his nafs saying, “O nafs! How will you bear the severe punishment of Allah Ta‘ala in the Hereafter?!”
After pondering and addressing oneself in this manner, one should sincerely repent and make taubah to Allah Ta‘ala. One should then make du‘aa to Allah Ta‘ala for the person regarding whom one had entertained evil thoughts saying, “O Allah! Bless him with the great bounties of this world and the next!”
One should repeat this procedure thrice in the day and night. Thereafter, if the evil thoughts still persist, then one should repeat it for a second and third day.
After adopting this procedure for three days consecutively, if the evil thoughts still persist, then one should go to the person regarding whom he has evil thoughts and say to him, “Without any basis or proof, I have begun to have evil thoughts regarding you. Please forgive me and make du‘aa for Allah Ta‘ala to remove this malady from my life.”
(Malfoozaat Hakeemul Ummat 23/366)
Source: Ihyaauddeen.co.za