Tirukkural-On Virtue-The Glory Of Renunciation-Kural 28

1. Niraimoli mandhar perumai nilathu
   Maraimoli kaati vidum.

One"s prophetic words alone will prove
Worth and greatness, in course of time.

The idea is that these words of God"s great men will live long after them and guide the people. It has been happening in this world, time and again, from the sixth Century B.C., which was really an era of spiritual awakening and certainly the watershed of human history as H G. Wells would out it. Isiah and Socrates, Gautama and Confucius are probably some of the sages Valluvar had in mind, besides the great Munis of our own land, when he said that the prophetic words of the great sages will ultimately prove their source.

Tolkapiyam has this to say on the subject conveying the same thought.