Musannaf Ibn Abi Shayba 9:1430

Abu al-Ahwas narrated to us, from Mughirah, from Ibrahim, regarding a man who married his foster sister while he did not know, then he learned of it after that. He said: The marriage is void. If he has consummated with her, then she has the dowry (mahr) for what he made lawful of her private part. And if he had not consummated with her, they are to be separated, and there is no dowry.