Do not feel secure of Allah's Punishment

O you who are deceived by false hopes! Satan was cursed and descended from the glorious abode by neglecting one prostration he was ordered to perform. Adam descended from Paradise because of a mouthful he ate. The criminal was separated by a handful of blood. Moreover, the adulterer is supposed to be killed in the most awful way because he committed an unlawful act. Flogging is enjoined on him who says a word of slander, or drinks a drop of liquor. He (Allah) ordered that one of your hands should be cut in case theft is committed, so do not feel secure, for He might cast you into Hellfire because of only one sin.
Allah, the Almighty says,

وَلَا يَخَافُ عُقْبَاهَا 

(Meaning of the Ayah), "And He (Allah) feared not the consequences thereof." (Ash-Shams, 91:15)

A woman was cast into Hellfire because of a cat. One may utter a word carelessly, which displeases Allah. This might be done without thinking about the gravity of the word, and then because of that he will be thrown into the Hellfire, like the distance between the east and the west. And one may obey Allah for sixty years, and at his death he misjudges, and this will be the reason for his being thrown into Hellfire. The person’s lifetime is judged by its end, and man's actions are regarded by their final deeds. Whoever breaks his ablution before the final salutation, surely his prayer becomes invalid, and whoever breaks his fast before sunset, surely his fast is invalid, and whoever is sinful at the end of his life, surely he will meet Allah in that state. If you give charity, surely you will find the blessings thereof, but beware of greed. How many times do you seek a good reward but it is rejected because of procrastination?

Verily, no salvation is found when faith is incomplete, when false hope is overestimated, when a disease has no remedy or visitor, when one insists on vain desires, when a sleeping heedless mind wanders blindly in wild intoxication, overwhelmed by its ignorance, feeling alienated from his Lord, and finding delight with his servants, and remembering people is his power and pleasure, while remembering Allah is his prison and death. To Allah he offers superficial acts of worship, and to people his devotion and trust are directed.

Taken from Al Fawaid by Ibn al-Qayyim