Homer

Calchas, son of Thestor, by far the best of the bird-diviners,
Who knew what is, what will be, and what has been before,
And guided the ships of the Achaeans into Ilium,
Through his prophecy, which Phoebus Apollo gave to him.
He, being well-disposed, addressed them and spoke,
The words of Calchas.

Achilles, dear to Zeus, you bid me to explain
The wrath of Apollo, the far-shooting lord?
Therefore I will speak; but you must agree, and swear to me,
That you will readily defend me with your words and your hands.
For I think I will anger a man who has great power
Over all the Argives, and whom the Achaeans obey.
The wrath of a powerful king is stirred.

For a king is stronger, when he is angry at a lesser man;
Even if he swallows his anger for that very day,
Yet he holds a grudge afterwards until he accomplishes it
In his breast; but you, say if you will keep me safe.
Swift-footed Achilles answered him and said:
Achilles promises Calchas immunity for speaking.

Take heart and speak the prophecy, whatever you know;
For by Apollo, dear to Zeus, to whom you, Calchas,
Praying, reveal prophecies to the Danaans,
No man, while I am alive and looking upon the earth,
Shall lay heavy hands upon you by the hollow ships,
Of all the Danaans, not even if you name Agamemnon,
Who now claims to be by far the best in the army.
And then the blameless seer took heart, and spoke,
He does not blame us for a vow, nor for a hecatomb.