From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer concurs with his father-in-law's ruling permitting the son to marry into the Jewish community. He argues that the father's testimony is worthless as it is based on mere conjecture, that the vast majority of Rishonim and Geonim hold a father is not believed to deny paternity without the mechanism of hekker bechorah, and that even under the minority Rambam view a sfek sfeika resolves in the son's favor.
Source: Shu"t Chasam Sofer EH I §13