You should know that all acts of disobedience are poison to the heart and cause its sickness and ruin. They result in its will running off course, against that of Allah, and so its sickness festers and increases. Ibn Al-Mubarak said:
I have seen wrong actions killing hearts, and their degradation may lead to their becoming addicted to them. Turning away from wrong actions gives life to the hearts, and opposing yourself is best for it.
Whoever is concerned with the health and life of his heart, must rid it of the effects of such poisons, and then protect it by avoiding new ones. If he takes any by mistake, then he should hasten to wipe out their effect by turning in repentance and seeking forgiveness from Allah, as well as by doing good deeds that will wipe out his wrong actions.
By the four poisons we mean unnecessary talking, unrestrained glances, too much food and keeping bad company. Of all the poisons, these the most widespread and have the greatest effect on a heart’s well being.
It was said that Allah revealed to Prophet ‘Uzayr (`alayhi sallam);
“O ‘Uzayr! If you committed a small sin, do not look at its smallness; rather look at Whom you have sinned against. If you are granted a small blessing, do not look at its smallness; rather look at the One who has granted it to you. And if a calamity befalls you, then do not complain against Me to My creation, just as I do not complain against you to My angels when your bad deeds are raised to Me.”
“The one who longs for Paradise will rush towards good deeds; the one who dreads Hell will put an end to his vices; the one who has a firm conviction in [the imminent arrival of] death will lose all his passions; and the one who really knows the dunya will find disasters easy to bear.”