A trilogy of tragedies, the Oresteia is about the end of the curse on the House of Atreus. It was written by the Greek playwright Aeschylus, who is often called the father of tragedy, in 458 BC.
The three plays are titled Agamemnon, The Libation Bearers and Eumenides. Together they tell about the end of the curse on the House of Aterus.
Agamemnon has Nyx mentioned twice. Her first appearance is in the beginning of the play where through Clytaemestra as a sort of shout of joy when declaring that Troy was under the control of the Achaeans.
"As herald of gladness, with the proverb, may Dawn (Eos/Hemera) be born from her mother Night (Nyx)!"
The second time occurs where Nyx and Zeus are honored by the Greeks who are celebrating the fall of Troy.
"Hail, sovereign Zeus, and you kindly Night (Nyx), you who have given us great glory, you who cast your meshed snare upon the towered walls of Troy, so that neither old nor young could overleap the huge enslaving net of all-conquering Destruction."
In The Libation Bearers she is merely mentioned. Orestes, the son of Agamemnon who had been sent away since infancy, meets with his sister Electra. They decide to avenge their father's death that had been carried out by their mother. Orestes and his friend Pylades pretend to be travelers from the land he had been sent away to. At the door he uses Nyx as reason for those dwelling inside the house to let him in quickly.
"Announce me to the masters of the house, for it is in fact to them that I come bearing news. And hurry, since the chariot of Night (Nyx) is speeding on with darkness, and it is time for wayfarers to drop anchor in some house friendly to all guests."
Nyx is mentioned most in Eumenides, as the Erinyes pose as her offspring. They, one form, first mention Nyx as their mother while they try to capture Orestes for committing matricide.
"As herald of gladness, with the proverb, may Dawn (Eos/Hemera) be born from her mother Night (Nyx)!"
"O mother Night (Nyx), hear me, mother who gave birth to me as a retribution for the blind and the seeing. For Leto's son dishonors me by snatching away this cowering wretch, a proper expiation for his mother's blood."
Coming upon Athena, the Erinyes introduce themselves, again as children of Nyx.
"Daughter of Zeus, you will hear it all in brief. We are the eternal children of Night (Nyx). We are called Curses in our homes beneath the earth."
Later on, when the trial of Orestes is waiting verdict, the Erinyes merely call to Nyx.
"O Night (Nyx), our dark Mother, do you see this?"
The votes cancelled each other out and Orestes is acquitted, the Erinyes lament over the result.
"Ah, cruel indeed are the wrongs of the daughters of Night (Nyx), mourning over dishonor!"
Athena gives them counsel, but they carry on like banshees... as one being, I suppose.
"Hear my anger, mother Night (Nyx); for the deceptions of the gods, hard to fight, have deprived me of my ancient honors, bringing me to nothing."
There is mention of the Moirai being their sisters due to having Nyx as their mother.
"I forbid deadly and untimely fate for men; grant to lovely maidens life with a husband, you that have the rightful power; you, divine Fates (Moirai), our sisters by one mother (Nyx), divinities who distribute justly, who have a share in every home, and whose righteous visitations press heavily at every season, most honored everywhere among the gods!"
Lastly, the Chorus of the Processional Escort end the play. The very first sentence of their parting choral is the following:
"Go on your way to your home, children of Night (Nyx): mighty, lovers of honor, children, yet aged, under kindly escort--you who dwell in the land, refrain from inauspicious speech!"
Book sources:
Aeschylus. Aeschylus. English translation by Herbert Weir Smyth, Ph. D. in two volumes. Cambridge, MA. Harvard University Press. 1926.