Apollodorus Library 3.15.7

[7] And journeying by way of Troezen, he lodged with Pittheus, son of Pelops, who, understanding the oracle, made him drunk and caused him to lie with his daughter Aethra. But in the same night Poseidon also had connexion with her. Now Aegeus charged Aethra that, if she gave birth to a male child, she should rear it, without telling whose it was; and he left a sword and sandals under a certain rock, saying that when the boy could roll away the rock and take them up, she was then to send him away with them.
  But he himself came to Athens and celebrated the games of the Panathenian festival, in which Androgeus, son of Minos, vanquished all comers. Him Aegeus sent against the bull of Marathon, by which he was destroyed. But some say that as he journeyed to Thebes to take part in the games in honor of Laius, he was waylaid and murdered by the jealous competitors. ¹ But when the tidings of his death were brought to Minos, as he was sacrificing to the Graces in Paros, he threw away the garland from his head and stopped the music of the flute, but nevertheless completed the sacrifice; hence down to this day they sacrifice to the Graces in Paros without flutes and garlands.