Yosef Karo

“ If a woman had relations with one kohen and married another kohen within three months, the child is disqualified from the priesthood. If a kohen has relations with a single girl and admits the child is his son, the son would be a kohen for all matters. ”

“ Here, our holy sages would raise him to priesthood status by himself.
Paragraph 2- If there was one witness that testified (that he is a kohen) , he is believed in order to feed him (the kohen) tithes in these times, and he can read the first Aliyah from the Torah and to raise his hands (for the congregation) . We would even elevate one nowadays to the priesthood from a document. How so? If the document stated, “So-and-so Kohen borrowed a maneh from so-and-so,” and witnesses are signed on the document, the individual is assumed to be a kohen like any other contemporary kohen. ”