Kural - 580

They drink with smiling grace, though poison interfused they see,
Who seek the praise of all-esteemed courtesy

Explanation
Those who desire (to cultivate that degree of) urbanity which all shall love, even after swallowing the poison served to them by their friends, will be friendly with them.

Tamil Transliteration
Peyakkantum Nanjun Tamaivar Nayaththakka
Naakarikam Ventu Pavar.