Allah, the Wise, has said:
خُذِ الْعَفْوَ وَ امُرْ بِالْعُرْفِ وَ أََعْرِضْ عَنِ الْجَاهِلِينَ
"Take to forgiveness and enjoin good and turn aside from the ignorant." 77]
Imam Ali (as) has said:
أَلْجَهْلُ أََصْلُ كُلِّ شَرٍّ.
"Ignorance is the root of all evils." 
Ignorance is a state that exists within humans and one who possesses it advances towards darkness, whereas one who keeps it away from himself reaches luminosity and acquires discernment and insight.
If a person chooses an incorrect path for himself and permits ignorance to guide him in his actions, he would be looked upon as a sinner and of the inmates of Hell. However, if he sets about on the correct path, and acts on the basis of knowledge and cognizance, he shall be of the delivered ones.
Being pleased and satisfied over one's actions is the key that opens the door of ignorance and the worst trait of an ignorant person is to claim to possess knowledge despite being ignorant.
An ignorant person, upon noticing his own faults, does not experience uneasiness and discomfort, and upon being advised, does not pay heed to it. Despite having knowledge of his ignorance (called simple ignorance) he still commits blunders.
1 – The Ignorant Commander
Yaaqub Laith Saffar (d. 265 ah) had a commander by the name of Ibrahim who despite being brave and courageous, was extremely ignorant.
Once during winter, Yaaqub ordered that his personal winter clothes be given to Ibrahim. Ibrahim had a servant by the name of Ahmad Ibn Abdullah, who had hatred towards him. When Ibrahim returned home, Ahmad asked him: "Don't you know that whomsoever Yaaqub Laith gives his personal clothes, he puts that person to death within that week?"
"Oh no! I was not aware of this. What is the way out?" asked Ibrahim.
Ahmad suggested to him that he should flee from there. He even agreed to accompany Ibrahim and arranged to meet him the following day. Later, Ahmad secretly went to Yaaqub Laith and informed him that Ibrahim was intending to flee to Sistan from where he would initiate a rebellion against Yaaqub Laith. Yaaqub pondered for a while and was on the verge of ordering his army to prepare for battle with Ibrahim when Ahmad made a request.
"Allow me to single-handedly bring Ibrahim's severed head before you," he said to Yaaqub.
Yaaqub Laith agreed. As Ibrahim was about to leave the city with his soldiers, Ahmad attacked him from behind, severed his head with his sword and brought it before Yaaqub Laith. Yaaqub handed the position of Ibrahim, his ignorant commander, to Ahmad who thus came to enjoy great esteem in his eyes.
2 – The Caliph's Ignorant Son
Mahdi Abbasi, the third Abbasid Caliph, had a son by the name of Ibrahim, who was a misguided individual. He showed intense enmity and malice towards Amirul Mo'minin (as) in particular.
Once he approached Maamun, the seventh Abbasid Caliph, and said to him:
"I saw Ali (as) in my dream. We were travelling together till we reached a bridge whereupon he granted me precedence in crossing it. I said to him: 'You claim to be the Commander of the Faithful, but we are more deserving of this status'. Ali (as) did not give me a proper answer."
"How did he answer you?" Mamun questioned.
"He simply greeted me several times by saying 'Peace, Peace'," replied Ibrahim.
"By Allah! He has answered you loud and clear," explained Maamun. Ibrahim was puzzled. Maamun went on, "He viewed you as an ignorant person, unworthy of responding to. This is because Allah, describing His special servants in the Qur'an, says: "And the servants of the Beneficent Allah are they who walk on the earth in humbleness, and when the ignorant address them, they say: Peace," which is (an expression) indicative of their lack of regard (with respect to the ignorant ones) and their (personal) greatness.
"Ali (as) looked upon you as an ignorant person and behaved with you as the Qur'an has recommended when dealing with ignorant persons."
3 – The Handsome but Ignorant Person
A pleasant, dignified looking person entered the court of Abu Yusuf Kufi (d. 182 ah), the judge of Harun Rashid who regarded him with great respect. The person sat in the gathering with such silence and dignity, that it prompted the judge to regard him as a person of great virtue. He asked the man if he wanted to say something.
"I seek an answer to a question," said the person.
"Whatever I know, I shall answer you," responded the judge humbly.
The person enquired, "When can a person break his fast?"
"When the sun sets," replied the judge.
"What if the sun does not set till midnight?"
Hearing this, the judge laughed out and said, "How appropriately has the poet Jarir Ibn Atiyyah (a poet of the Umayyad period, who had died in the year 110 ah) said:
Silence is a beauty for a person who is weak and ignorant; surely, the intelligence of a person is known by his speech, just as his lack of intelligence also becomes manifest as a result of his speech."
Thus, the judge came to know of the ignorance of the good-looking person.
4 – Qais Ibn asim
Qais Ibn 'asim was a tribal leader during the Age of Ignorance but he later accepted Islam.
Once, during his old age, in order to seek ways to make amends for his past misdeeds, he arrived in the presence of the Noble Prophet (sa) and said: "In the past, ignorance had instigated numerous fathers to bury their innocent daughters alive. I too, had buried twelve of my daughters alive at short intervals. My wife gave birth to my thirteenth daughter in secret and, making it appear to me as if it had been a stillborn child, she secretly sent the infant to her own relatives (for upbringing).
Years passed till one day I returned home suddenly and unexpectedly from one of my trips, only to find a small girl in my house. Since she resembled my children, I found myself perplexed till eventually I came to know that she was my daughter.
I immediately took hold of the girl, who was weeping profusely, and took her to a remote location, refusing to permit myself to be affected by her wailing. She kept pleading, 'I shall return to my maternal uncles and shall never come to your house again', but I paid no heed to her request and buried her alive."
When he had narrated this, Qais noticed that tears flowed down the Noble Prophet's (sa) eyes and heard him murmuring: "One who does not look upon others with mercy shall not be looked upon with mercy."
Then turning to Qais, he said, "You have difficult days ahead of you!"
"What should I do to lessen the burden of my misdeeds?" inquired Qais.
"For every daughter killed, set free a slave-girl," replied the Noble Prophet (sa).
5 – A Long Beard
Jahidh Basri, (d. 249 ah) who has a book to his name in every branch of science, states: "Maamun Abbasi and a few other individuals had gathered together and were engaged in conversation.
"A person who sports a long beard is stupid and foolish," one of them remarked.
Some others objected by saying, "On the contrary, we have seen individuals growing long beards but who were clever and intelligent."
"Impossible!" exclaimed Maamun.
At that moment, a man with a long beard and riding a camel came towards them. Maamun, in order to prove his point, summoned the person and asked him what his name was.
"Abu Hamdwaih", replied the man.
"What is your agnomen?" asked Maamun.
Maamun said to those around him, "A person who is so ignorant so as to be unable to differentiate between a name and an agnomen, all his other acts would also be characterized with the same ignorance."
Turning to the man once again, he asked, "What work do you do?"
"I am a jurisprudent and an expert in various sciences. If the king desires, he can question me."
"A person sold a sheep to another person, who took the animal in his possession. But he had not yet paid the price of the animal when it released its dung, which fell into the eyes of another person, blinding him. Under the circumstances, whose obligation is it to pay the compensation for the injury caused?" asked Maamun.
The person with the long beard reflected for a while and then said: "The compensation should be paid by the seller and not the purchaser." Those around wanted to know why.
"It is because the seller did not inform the purchaser that he had placed a catapult inside the rear of the sheep, which it used for hurling stones in order to protect itself," explained the person.
Hearing this, Maamun and those around him burst out in laughter. The man was given some money and he left.
"The truth of my statement has become manifest before you that the elders have stated): A long-bearded person is a dimwit," said Maamun.
 Noble Qur'an, Suratul ھ`raf (7), Verse 199
 Ghurar al-Hikam, Tradition 819
 Namunah-e-Maaarif, Volume 4, Page 93
 Noble Qur'an, Suratul Furqan (25), Verse 63: وَ إِذا خاطَبَهُمُ الْجاهِلُونَ قالُوا سَلاماً
 Hikayat-ha-e-Shanidani, Volume 2, Page 20; Safinatul Bihar, Volume 1, Page 79
 وَ فيِ الصَّمتِ زينٌ لِلْغَبي
 Lataif al-Tawaf, Page 412
 مَن لاَ يَرْحَم لاَ يُرْحَم
 Dastan-ha Wa Pand-ha, Volume 1, Page 15; Jahiliyyat Wa Islam, Page 632
 There are traditions that censure the keeping of a long beard. One of the things, which Imam Ali (as) mentioned in his criticism of the people of Basrah, was their long beards. The Noble Prophet (sa) regarded not sporting a long beard as being one of the felicities of man. (Safinatul Bihar, Volume2, Page 509
 Jawamea al-Hikayat, Page 300