Pindar, Py (Pythian) 12.14-15:
…he [Perseus] repaid Polydectes with a deadly wedding-present for the long  slavery of his mother and her forced bridal bed… (original Greek)
AP (Palatine Anthology [Greek Anthology]) 3.11 (Greek Anthology, ed. W.R. Paton, vol. 1 , pp. 100-101, Greek and translation):
In 11, Polydektes, king of the Seriphians, petrified by Perseus with the head of the Gorgon after sending him off for the sake of marriage with his mother, received himself, by the providence of Justice, the very death which he devised to happen to another:
Even you, Polydektes, dared to pollute the couch of Danae, repaying Zeus with infamous bedding; for which Perseus unleashed here the eyes of the Gorgon, stoneworking your limbs, pleasing his mother (translation by Silvio Curtis).
He [Dictys] took them to King Polydectes, who married Danaë and brought up Perseus in the temple of Minerva. When Acrisius discovered they were staying at Polydectes’ court, he started out to get them, but at his arrival Polydectes interceded for them, and Perseus swore an oath to his grandfather that he would never kill him. When Acrisius was detained there by a storm, Polydectes died, and at his funeral games the wind blew a discus from Perseus’ hand at Acrisius’ head which killed him (original Latin).