Kural - 884

If secret enmities arise that minds pervert,
Then even kin unkind will work thee grievous hurt

Explanation
The secret enmity of a person whose mind in unreformed will lead to many evils causing disaffection among (one's) relations.

Tamil Transliteration
Manamaanaa Utpakai Thondrin Inamaanaa
Edham Palavum Tharum.