Allah, the Exalted, says:

"And follow not (O man, i.e., say not or do not or witness not) that of which you have no knowledge.'' (17:36)

"Not a word does he (or she) utter, but there is a watcher by him ready (to record it).'' (50:18)

Abu Hurairah (radiallahu anh) said: The Prophet (salallahu 'alayhi wa sallam) said, "It is enough for a man to prove himself a liar when he goes on narrating whatever he hears.''
[Muslim]

We learn from this Hadeeth that it is not fair to accept everything one hears as true without verifying it. Nor it is right to communicate it to others because it is quite possible that what one has heard is untrue and by communicating it to others, he adds it to his own lies.

Samurah (radiallahu anh) reported: The Messenger of Allah (salallahu 'alayhi wa sallam) said, "He who relates from me something which he deems false is one of the liars.''
[Muslim]

In some of the narrations of this Hadith, the word used is "Kadhibain'' which means "two liars'' One is that person who tells a lie and attributes his statement to the Prophet (salallahu 'alayhi wa sallam). The second is that person who conveys it to others. Thus, this Hadeeth has a stern warning for those preachers who feel no hesitation in relating false and fabricated Ahadeeth.

Asma' (radiallahu anh) reported: A woman came to the Messenger of Allah (salallahu 'alayhi wa sallam) and said: "I have a co-wife. Is there any harm for me if I give her the false impression of getting something from my husband which he has not in fact given me?'' The Messenger of Allah (salallahu 'alayhi wa sallam) said, "The one who creates a false impression of receiving what one has not been given is like one who wears two garments of falsehood.''
[Al-Bukhari and Muslim]

Some people disguise themselves as pious to create a false impression of their piety; some put up the appearance of scholars to establish their scholarship; and some take to highly expensive clothes to give the impression of being rich. Since these things are fabricated and false, they constitute great sins. One should live as one really is.