"...I guarantee a home in the middle of Jannah for the one who abandons lying, even in jest."
(Abu Dawood, Adab 7)
A lie is an expression of blindness, fear and helplessness in the face of truth. Lies are the foundation on which the building of discord is erected.
Why would a person resort to lying? Why would one place a rock on the foundation of a building if the ceiling is buried deep in the ground? Is it to hide from the truth?
"Abandon what you doubt and prefer that about which you have no doubts," says the Messenger of Allah (pbuh), "For truth is comforting to the soul and lies are doubtful."(At-Tirmidhi, Qiyamah 60).
From whom is the liar hiding the truth?
Only from themselves! A lie feeds all other bad deeds, because it paves the way for back-biting, holding grudges, slander, disclosing the secrets of others, failure to honor promises and creating fitna (dissension); it makes all these seem harmless and one can fail to be aware of the evil they are committing. Lies, if not refrained from, even if only one word, accumulate to strike the last blow to one's faith; a veil becomes drawn between the truth and human beings.
"Always be truthful, for truthfulness leads to righteousness and righteousness leads to Paradise. If you are always truthful and seek truthfulness, God records you as such. Never lie, for lying leads to shamefulness and shamefulness leads to Hell. If you insist on lying and seek deceit, God records you as such." (Bukhari, Adab 69)
Who does a person cheat if they turn the truth upside down?
Their Creator! He whom created matter based on truth! Life is but a trust to mankind, and so is what one hears, sees, one's possessions earned through work, all one owns in sincerity and their body. Everything that is borrowed must be used in the fashion desired by its Owner; it must be used without being sullied by sin and returned in a pure form.
Every morning the parts of a person's body warn the tongue, saying: "Fear God concerning us. For if you are true, we will be true and straight; if you are crooked, we will also deviate." [At-Tirmidhi, Zuhd, 61).
To God's servants! Lies are a wall that is erected between us and the sun; one who lies erects a wall in front of the truth. Lies sully our ears, impair our vision and mar our hearts. If what is promised is a lie, then it destroys our dreams and destroys our sense of trust. Thus, the faculties of a body can easily become separated. Lies steal our future and our hopes.
The sirat al-mustaqim (the righteous path) is the only road and Islam is the only method that leads to the truth. Allah Almighty addresses Prophet Muhammad and believers when He says: "So, adhere to that which you are commanded to do, - you and those who have turned to Allah along with you - and do not transgress, for He is perusing everything you do!" (Surah Huud (11): 112).
The path becomes apparent through the righteousness of its traveler. Even a small action that creates a fear of crookedness in the path will become a roadblock for a believer. Even if said in jest!