Actually I prefer referring it as Test First Design with an emphasis on Design. Whatever, while scanning through my book marks, I found this nugget of wisdom.

E.W.Dijkstra Archive: Dijkstra: The Humble Programmer.

The only effective way to raise the confidence level of a program significantly is to give a convincing proof of its correctness. But one should not first make the program and then prove its correctness, because then the requirement of providing the proof would only increase the poor programmer’s burden. On the contrary: the programmer should let correctness proof and program grow hand in hand.

Is this the earliest referrence?