Apollodorus Library 3.7.6

[6] Being apprized of Alcmaeon's untimely end and courted by Zeus, Callirrhoe requested that the sons she had by Alcmaeon might be full grown in order to avenge their father's murder. And being suddenly full-grown, the sons went forth to right their father's wrong. ¹ Now Pronous and Agenor, the sons of Phegeus, ² carrying the necklace and robe to Delphi to dedicate them, turned in at the house of Agapenor at the same time as Amphoterus and Acarnan, the sons of Alcmaeon; and the sons of Alcmaeon killed their father's murderers, and going to Psophis and entering the palace they slew both Phegeus and his wife. They were pursued as far as Tegea, but saved by the intervention of the Tegeans and some Argives, and the Psophidians took to flight.