Kural - 669

Though toil and trouble face thee, firm resolve hold fast,
And do the deeds that pleasure yield at last

Explanation
Though it should cause increasing sorrow (at the outset), do with firmness the act that yield bliss (in the end).

Tamil Transliteration
Thunpam Uravarinum Seyka Thunivaatri
Inpam Payakkum Vinai.