Falsehood is to speak contrary to facts.
For a person to be regarded as a liar it will suffice that he narrates every rumour without investigating whether it is a fact or not. Rasulullah Sallallahu alayhi wasallam ordered abstention from lies because falsehood and immorality are complementary partners and both will be in Jahannam . Nabi Sallallahu alayhi wasallam said that false evidence is equivalent to shirk . Rasulullah Sallallahu alayhi wasallam was shown a man whose cheeks were being repeatedly slit from ear to throat. The cheeks would heal immediately upon having been slit and the process of slitting would be repeated.