Laudator Temporis Acti

Philostorgius, Church History 7.1c = Passion of Artemius 35 (Artemius speaking to Julian, tr. Philip R. Amidon):

Know therefore that the strength and power of Christ is invincible and unconquerable. You yourself are certainly convinced of this from the oracles that the physician and quaestor Oribasius recently brought you from the Apollo in Delphi. But I will repeat the oracle to you, whether you wish to hear it or not. It runs as follows:

Go tell the king the wondrous hall is fallen to the ground.
Now Phoebus has a cell no more, no laurel that fortells,
No talking spring; the water that once spoke is heard no more.

George Cedrenus, Compendium Historiarum, ed. I. Bekker, Tomus Prior (Bonn: Weber, 1838 = Corpus Scriptorum Historiae Byzantinae, 34), p. 532 (304 A, my translation):

He [Julian] sends his physician and quaestor Oribasius to raise up Apollo's temple at Delphi. After departing and undertaking the work, he receives an oracle from the god:

Say to the king, the cunningly wrought hall has fallen to the ground,
Phoebus no longer has a hut, or prophetic laurel tree,
Or talking spring; extinguished is also the talking water.

Translation of the oracle by William Marris:

Tell ye the king: the carven hall has fallen in decay:
    Apollo hath no chapel left, no prophesying bay,
No talking spring. The stream is dry that had so much to say.

Another translation, by Algernon Charles Swinburne, from his poem "The Last Oracle":

Tell the king, on earth has fallen the glorious dwelling,
And the watersprings that spake are quenched and dead.
Not a cell is left the God, no roof, no cover;
In his hand the prophet laurel flowers no more.

Another translation, by Kenneth Rexroth:

Go tell the King: the daedal
Walls have fallen to the earth,
Phoibos has no sanctuary,
No prophetic laurel, no
Speaking spring. The garrulous
Water has dried up at last.

The Greek:

εἴπατε τῷ βασιλῆι· χαμαὶ πέσε δαίδαλος αὐλά.
οὐκέτι Φοῖβος ἔχει καλύβαν, ὀυ μάντιδα δάφνην,
οὐ παγὰν λαλέουσαν. ἀπέσβετο καὶ λάλον ὕδωρ.

Many authorities regard the oracle as a forgery. It is "quasi-historical response" number 263 in Joseph Fontenrose, The Delphic Oracle (Berkeley: University of California Press, 1978), p. 353. Some additional bibliography (most of which I haven't seen):

• E.A. Thompson, "The Last Delphic Oracle," Classical Quarterly 40 (1946) 35-36
• C.M. Bowra, "ΕΙΠΑΤΕ ΤΩΙ ΒΑΣΙΛΗΙ," Hermes 87 (1959) 426-435; rpt. in his On Greek Margins (Oxford: Clarendon Press, 1970), pp. 233-252
• Averil M. Cameron, "Agathias and Cedrenus on Julian," Journal of Roman Studies 53 (1963) 91-94
• Georgios Fatouros, "ΕΙΠΑΤΕ ΤΩΙ ΒΑΣΙΛΗΙ," Hermes 124 (1966) 367-374
• Timothy E. Gregory, "Julian and the Last Oracle at Delphi," Greek, Roman and Byzantine Studies 24 (1983) 355-366
• A. Markopoulos, "Kedrenos, Pseudo-Symeon, and the Last Oracle at Delphi," Greek, Roman and Byzantine Studies 26 (1985) 207-210
• Bernadette Cabouret, "Julien et Delphes: la politique religieuse de l'empereur Julien et le 'dernier' oracle," Revue des études anciennes 99 (1997) 141-158