Sappho 206 LP (Poetarum Lesbiorum Fragmenta, ed. E. Lobel and D. L. Page ):
Some would have it that seven boys and seven girls were taken, whom Theseus freed together with himself. Plato says so in the Phaedo (58a), Sappho in her lyrics, Bacchylides in his dithyrambs (17. 1 ff.) and Euripides in his play Hercules (1326) (translated by Nick Gardner).
Bakchylides Ode 17:
A dark-prowed ship, carrying Theseus, steadfast in the din of battle, and twice seven splendid Ionian youths, was cleaving the Cretan sea;  for northern breezes fell on the far-shining sail, by the will of glorious Athena, shaker of the aegis. And the holy gifts of Cypris with her lovely headband scratched the heart of Minos.  He no longer kept his hand away from the maiden; he touched her white cheeks. And Eriboea cried out  to the descendant of Pandion with his bronze breastplate. Theseus saw, and he rolled his dark eyes under his brows; cruel pain tore his heart,  and he spoke: “Son of greatest Zeus, the spirit you guide in your heart is no longer pious. Hero, restrain your overbearing force. Whatever the all-powerful fate of the gods  has granted for us, and however the scale of Justice inclines, we shall fulfill our appointed destiny when it comes. As for you, hold back from your oppressive scheme. It may be that the dear  lovely-named daughter of Phoenix went to the bed of Zeus beneath the brow of Ida and bore you, greatest of mortals, but I too was borne by the daughter of rich Pittheus,  who coupled with the sea-god Poseidon, and the violet-haired Nereids gave her a golden veil. And so, war-lord of Knossos,  I bid you to restrain your grievous violence; for I would not want to see the lovely immortal light of Dawn if you were to subdue one of these young people against her will.  Before that we will show the force of our arms, and what comes after that a god will decide.” So spoke the hero, excellent with the spear; and the sailors were astonished at the man’s extraordinary  boldness. The son-in-law of Helios was angered in his heart, and he wove a new scheme, and spoke: “Father Zeus, great in strength, hear me! If indeed the white-armed Phoenician girl bore me to you,  now send forth from the sky a fire-haired lightning bolt, a conspicuous sign. And you, if Troezenian Aethra bore you to Poseidon the earth-shaker,  bring this splendid gold ornament on my hand back from the depths of the sea, casting your body boldly down to your father’s home. And you shall see whether my prayers are heard  by the son of Cronus, lord of the thunder and ruler of all.” And Zeus, great in strength, heard his blameless prayer, and brought about a majestic honor for Minos, wanting it  to be seen by all for the sake of his dear son; he sent the lightning. And the hero, steadfast in battle, seeing the marvel which pleased his spirit, stretched his hands to the glorious sky and said, “Theseus,  you see Zeus’ clear gifts to me. It is your turn to leap into the loud-roaring sea. And your father lord Poseidon, son of Cronus, will grant you supreme  glory throughout the well-wooded earth.” So he spoke. And Theseus’ spirit did not recoil; he stood on the well-built deck, and leapt,  and the precinct of the sea received him willingly. And the son of Zeus was astonished in his heart, and gave an order to hold the ornate ship before the wind; but fate was preparing another path.  The swift-moving ship hurtled forwards; and the north wind, blowing astern, drove it along. But the … race of Athenian youths was afraid, when the hero jumped into the sea,  and they shed tears from their lily eyes, awaiting grievous compulsion. But sea-dwelling dolphins swiftly carried great Theseus to the home of his father, lord of horses;  and he came to the hall of the gods. There he saw the glorious daughters of prosperous Nereus, and was afraid; for brightness shone like fire from their splendid limbs,  and ribbons woven with gold whirled around their hair. They were delighting their hearts in a dance, with flowing feet. And he saw in that lovely dwelling the dear wife of his father,  holy, ox-eyed Amphitrite. She threw a purple cloak around him and placed on his curly hair a perfect wreath,  dark with roses, which once deceptive Aphrodite had given her at her marriage. Nothing that the gods will is unbelievable to sensible men. Theseus appeared beside the ship with its slender stern. Oh,  from what thoughts did he stop the war-lord of Knossos, when he emerged unwetted from the sea, a marvel to all, and the gifts of the gods shone on his body.  The splendid-throned maidens cried out with new-founded joy, and the sea resounded. Nearby the young people sang a paean with lovely voices.  God of Delos, may the choruses of the Ceans warm your heart, and may you grant god-sent noble fortune (original Greek).
Isokrates 10.Helen 27:
At about the same time appeared the monster reared in Crete, the offspring of Pasipha, daughter of Helius, to whom our city was sending, in accordance with an oracle’s command, tribute of twice seven children. When Theseus saw these being led away, and the entire populace escorting them, to a death savage and foreseen, and being mourned as dead while yet living, he was so incensed that he thought it better to die than to live as ruler of a city that was compelled to pay to the enemy a tribute so lamentable (original Greek).
Diodorus Siculus 4.60.4-5:
 And marrying Pasiphaê, the daughter of Helius and Cretê, he begat Deucalion and Catreus and Androgeos and Ariadnê and had other, natural, children more in number than these. As for the sons of Minos, Androgeos came to Athens at the time of the Panathenaic festival, while Aegeus was king, and defeating all the contestants in the games he became a close friend of the sons of Pallas.  Thereupon Aegeus, viewing with suspicion the friendship which Androgeos had formed, since he feared that Minos might lend his aid to the sons of Pallas and take from him the supreme power, plotted against the life of Androgeos. Consequently, when the latter was on his way to Thebes in order to attend a festival there, Aegeus caused him to be treacherously slain by certain natives of the region in the neighbourhood of Oenoê in Attica (original Greek).
Edited by Nick Gardner, Graduate Research Assistant, Department of Classics, Univ. of Georgia, April 24, 2016.