Thirukkural-On Virtue-Avoidance of Fraud-Kural-288

Just as virtue reigns in the heart, regulated by a correct sense of values,
Fraud lives in the heart that is full of deceit.

In a heart regulated by the code of righteousness virtue reigns; so too, in a heart full of deceit fraud stays on. This is an instance of the literary method of poetic counterbalance adopted by Valluvar very often to stress the characteristics of two opposites.

The following line of the Bible is relevant in this context:
'Deceit is in the heart of those who devise evil…"
(Proverbs 12:20)

it is also interesting to study here the Talmudian definition of a saint and a wicked man.

'He who says, what is mine is yours and what is yours is yours is a Saint. He who says, what is yours is mine and what is min is mine, is a wicked man".
(Talmud)