"For people who speak falsely,

Who transgress in this one way,

And who reject the world beyond,

There is no evil they won't do."

Dhammapada verse 176

"The Buddha was sitting with his son Rahula who was seven at the time. The Buddha asked Rahula if he saw the few drops of water left in the ladle the Buddha was holding.

Rahula replied that he did. The Buddha tells Rahula “that is how little understanding one has who tells deliberate lies.”

The Buddha then tosses away the few drops of water and tells Rahula 'A person who feels no shame in telling deliberate lies has tossed away their mindfulness.'

The Buddha then turns the ladle upside down and tells Rahula 'A person who feels no shame in telling deliberate lies has turned their mindfulness upside down.'

The Buddha then shows Rahula the empty ladle and says 'Whoever feels no shame in telling a deliberate lie is as empty and hollow as this ladle. Anyone who feels no shame in telling deliberate lies is capable of any wrong-doing. Train yourself, Rahula, ‘I will not tell a deliberate lie for any reason, even jokingly.'

The Buddha asks Rahula if he knows what a mirror is for and Rahula replies 'for reflection, sir.' The Buddha responds “In the same way your thoughts, words and deeds must be done with constant reflection. Reflect in this manner, Rahula: ‘Is this thought, word or deed skillful? Will it lead to harm for myself or others, or will it lead to release? Will this thought, word or deed bring more suffering for myself or others, or will it have a peaceful result? If upon reflection your thoughts words and deeds will have peaceful results then this is fit for you and fit for a person developing understanding.'

'Rahula, all those who purify their minds through continual reflection (mindfulness) will do so in just this way. Rahula you should train yourself in just this way through continual mindfulness of your thoughts, words, and deeds.”

RAHULAVADA SUTTA (MN 61)