Tirukkural is an ancient Tamil treatise by the poet Valluvar which talks about different subjects. Here are four verses that describe the nature of friendship. They have been presented as a viruttham in the ragas Malayamarutham, Latangi, Begada and Shanmukhapriya. Shwetha Narasimhan plays the violin.
The verses and their meaning are given below. Source: http://www.ytamizh.com/thirukural
குறள் 781:
செயற்கரிய யாவுள நட்பின் அதுபோல்
வினைக்கரிய யாவுள காப்பு.
Explanation: What things are there so difficult to acquire as friendship? What guards are there so difficult to break through by the efforts (of one’s foes)?
குறள் 782:
நிறைநீர நீரவர் கேண்மை பிறைமதிப்
பின்னீர பேதையார் நட்பு.
Explanation: The friendship of the wise waxes like the new moon; (but) that of fools wanes like the full moon.
குறள் 783:
நவில்தொறும் நூல்நயம் போலும் பயில்தொறும்
பண்புடை யாளர் தொடர்பு.
Explanation: Like learning, the friendship of the noble, the more it is cultivated, the more delightful does it become.
குறள் 784:
நகுதற் பொருட்டன்று நட்டல் மிகுதிக்கண்
மேற்செனறு இடித்தற் பொருட்டு.
Explanation: Friendship is to be practised not for the purpose of laughing but for that of being beforehand in giving one another sharp rebukes in case of transgression.
Chitra Srikrishna 