Musannaf Ibn Abi Shayba 9:1361

Abu Bakr narrated to us, he said: Hafs narrated to us, from Ash'ath, from al-Hasan, regarding a woman who marries while she has a husband. He said: If she brings him [the child] and he [the husband] doubts it, then it belongs to the first. And if she brings him and he does not doubt it, then it belongs to the latter.