Allah, the Wise, has said:
سَمَّاعُوْنَ لِلْكَذِبِ أََكَّالُونَ لِلسُّحْتِ
"(They are) listeners of falsehood, devourers of what is forbidden." 
Imam 'Askari (as) said:
جُعِلَتِ الْخَباَئِثُ کُلُّهاَ فِي بَيْتٍ وَ جُعِلَتْ مِفْتاَحَهاَ الْکِذْبُ
"All the evils have been placed in a house and lies have been made its key." 
Speaking untruths - trivial or great, in jest or in seriousness - is not permitted since it has been said: "All the evils have been placed in a house and lies have been made its key", it becomes very important to abstain from this act.
Since lies refer to unrealities and one who utters lies, neither does so for the purpose of exaggerating his point nor for effecting reconciliation between two warring factions, it causes the angels to distance themselves from him. It brings about destruction of his faith, reduction in his livelihood, and humiliation and disgrace in the eyes of the people - to the extent that if untruths are ascribed to Allah and the Noble Prophet (sa) in the month of Ramadhan, it even results in the invalidation of fasts.
1 – Walid Ibn ‘Uqbah
Abi Mu'eet Walid Ibn 'Uqbah was a Muslim who initially appeared to be such a righteous individual that the Noble Prophet (sa) even assigned him the responsibility of collecting the zakat and sadaqat from the tribe of Bani Mustalaq. When the people of the tribe came to know of the arrival of a representative of the Noble Prophet (sa), they came forward to welcome him.
During the Age of Ignorance, there had existed enmity between Walid and this tribe, and seeing the people come towards him in a large group, thought that they had prepared themselves to kill him. He quickly turned back and returned to Madinah.
He went to the Noble Prophet (sa), and told him that the people of the tribe were not willing to pay their zakat, which obviously was not true.
The Noble Prophet (sa) was upset to hear this and made up his mind to despatch an army towards the tribe, when Allah revealed the following verse: "O you who believe! If an evil-doer comes to you with a report, look carefully into it)(to ascertain the veracity of it)."
After the revelation of this verse, the liar Walid came to be recognized as a corrupt person.
"He is of the inmates of Hell," the Noble Prophet (sa) said about him.
Walid later teamed up with 'Amr Ibn aھs and the two would consume intoxicants and harboured feelings of animosity towards the Noble Prophet (sa) and Amirul Mu'mineen (as).
The third caliph, during his caliphate, appointed him the governor of Kufah and one morning, in a state of intoxication, he led the morning congregational prayers by performing four-rak'ats instead of the stipulated two.
2 – Hunger and Lies
Asma Bint aUmais, reported: "On the night of aھishah's marriage with the Noble Prophet (sa), a few ladies and I were with her, dressing her up. When we went to the house of the Noble Prophet (sa), we did not find any food except a single bowl of milk. He drank a little milk from it and then handed it to Aishah. Overcome by bashfulness, she did not take it.
"Do not refuse the Prophet of Allah; take the bowl and drink the milk," I said to her. Shyly, she took the bowl and drank some milk from it.
"Pass on the bowl to your companions in order that they may drink from it too," the Noble Prophet (sa) instructed her.
The ladies, who were with us, said, "We are not hungry."
Hearing this, the Noble Prophet (sa) remarked, "Do not gather hunger and lies together (i.e. why do you lie while at the same time, you remain hungry?).
"O' Prophet of Allah! If we were to possess an appetite for something but we deny having it, would we have uttered a lie?" I inquired.
"A lie, even if trivial and insignificant, is recorded in the Book of Deeds," stated the Noble Prophet (sa).
3 – The Lies of the Poet
Khusro Hirawi was a contemporary of 'Abd al-Rahman Jami, and the following verse is his composition: "The flower of your face has watered the garden of beauty, and it has been the curls of your hair that have imparted the twists to the violets."
It has been reported that he said: "My father, who had prepared food on the occasion of my circumcision, had utilized three hundred kilograms of powdered saffron." Those present around him asked him what food he had put such a large quantity of saffron in.
"One hundred and twenty kilos in saffron-seasoned rice, ninety kilos in pea-soup, thirty kilos in fricassee and thirty kilos in sweat-meat," he replied.
"This sums up to two hundred and seventy kilos; what about the other thirty kilos?" his companions pointed out.
Bewildered, Khusro thought for a while after which he raised his head and lied with great exuberance: "I remember now. He used the final thirty kilos in 'quttab'!" ) and 
4 – Zainab the Great Liar
During the caliphate of Mutawakkil Abbasi, a woman claimed that she was Zainab, the daughter of Fatimah Al-Zahra .
"Years have passed since the time of Zainab, but you appear to be young," said Mutawakkil to her.
"The Noble Prophet (sa) caressed my head and prayed that every forty years I should become young again!" said the woman.
Mutawakkil called for the elders from the progeny of Abu ±alib, Abbas and the Quraish and placed the issue before them. All of them unanimously averred that the woman was lying because Zainab had died in the year 62 ah.
Zainab, the great liar retorted, "They are the ones who lie. I had concealed myself from the people and none knew of my whereabouts until today."
"You must establish the falsity of her claims by means of proofs," insisted Mutawakkil to the elders.
"Ask Imam Hadi (as) to prove false her claims," they advised. Mutawakkil called for the Imam (as) and informed him of the issue.
"She lies, for Zainab had died in such and such year," said the Imam (as).
"Present your evidence to prove false her claim," Mutawwakil demanded.
The Imam (as) said, "The flesh of the children of Fatimah is forbidden upon the wild beasts; send her before the lions if she speaks the truth!"
Mutawakkil turned to the woman for an answer.
"In this way, he desires to kill me," said the woman.
"A number of people from the progeny of Fatimah are present here. You can send whoever you desire (before the wild beasts)," responded the Imam (as).
The narrator states: "The faces of all the sadat present in the gathering turned pale. Some said, "Why does he not go himself instead of referring to others?"
Mutawakkil asked the Imam (as) why he himself was not going before the lions. The Imam (as) instantly agreed to go. Mutawakkil ordered for a ladder, and the Imam (as) entered into the enclosure where the lions were maintained. The wild beasts, in submission and humility, placed their heads on the ground before the Imam (as) and he in turn, caressed their heads. A little later he ordered them to move aside and all of them obeyed!
Mutawakkil's minister advised him, "Ask Imam Hadi (as) to come out immediately for if the people witness this miracle, all of them would flock to him."
The ladder was laid again and the Imam (as) climbed out.
"Whoever is of the children of Fatimah should come forward and sit amongst the wild beasts," proclaimed Imam Hadi (as).
The woman (having witnessed the scene) admitted, "O' Imam! My claims are false. I am the daughter of a certain destitute, and poverty forced me to resort to this deception."
Mutawakkil ordered his guards to throw the woman to the lions but his mother intervened and interceded for Zainab who was then pardoned."
5 – The Plain Lie of Amir Husain
Sultan Husain Bayaqra who ruled over Khorasan and Zabolistan, and Yaaqub Mirza who ruled over Azerbaijan, were friends who frequently sent letters and gifts to each other.
Once, Sultan Husain handed over some exquisite and valuable items to a person named Amir Husain Abyurdi and instructed him to pick the book 'Kulliyat Jami' from the library and present it to Sultan Yaaqub Mirza along with the other items.
Amir Husain approached the librarian and asked for the book, but the librarian erroneously handed him Muhyuddeen 'Arabi's book, Al-Futoohat Al-Makkiyyah, which greatly resembled the book Kulliyat Jami' in size and volume. Amir Husain set out for Azerbaijan and arriving in Yaaqub Mirza's presence, handed him Sultan Husain's letter and presents.
After going through the contents of the letter, Yaaqub inquired after the health of Sultan Husain and the other ministers of the Sultanate. He then asked about Amir Husain's health and with reference to the long two-month journey that Amir Husain had undertaken to reach him, he said: "You must surely have had a companion to make your journey pleasant."
"Yes, I had in my possession the book 'Kulliyat Jami', which has been transcribed recently. Throughout the journey, I was engaged in reading it and thoroughly enjoyed it," replied Amir Husain.
As soon as Yaaqub Mirza heard the name of Kulliyat Jami', he said, "I had been desirous of this book and am extremely pleased that you have brought it." Amir Husain sent one of his servants to bring the book and when it was brought, he handed it to Yaaqub Mirza. When Yaaqub Mirza opened the book, he observed that it was Al-Futoohat Al-Makkiyyah. He turned to Amir Husain and asked, "This is not Kulliyat Jami' - why did you lie?"
Amir Husain, embarrassed and ashamed, did not even wait to take the reply of the letter, but immediately set out for Khorasan.
"When my lie had been exposed, I wished that I had died," said Amir Husain later on.
 Noble Qur'an, Suratul Ma`idah (5), Verse 42
 Jamea al-Saaadat, Volume 2, Page 323
 Ihya al-Qulub, Page 151
 Noble Qur'an, Suratul Hujarat (49), Verse 6 (ياَ اَيُّهاَ الَّذِينَ آمَنُوا اِن جاَءَکُم فاَسِقٌ بِنَبَأٍفَتَبَيَّنُوا
 Safinatul Bihar, Volume 2, Page 361
 Ibid., Page 688
 Shanidani-ha-e-Tarikh, Page 294; Mahajjatul Baiza, Volume 5, Page 249
 A sweetmeat (Tr)
 Lataif al-Tawaif, Page 414
 Muntahal Aamal, Volume 2, Page 368
 Khazinatul Jawahir, Page 640; Tarikh Jaib al-Sair