Shulchan Arukh Even HaEzer · Siman 151

English

The scribe wrote the receipt [for divorce] and the divorce document, and made a mistake and gave the receipt to the man and the divorce document to the woman, and they gave them to each other and they were under the impression that they were divorced, and afterwards the husband objected to say she wasn't divorced, that he only gave her the receipt and the divorce document is still in his hands, if she didn't [re]marry yet, he's believed, and he should divorce her now and she will be permitted onwards. And if he didn't divorce her, and she gets up and [re]marries, she leaves this one and that one (first and second husbands), and all of the 13 ways [apply] to her. And if the husband did not object until after she [re]marries, he's not believed to forbid her, and she retains the status of a divorcee, since we "hang" [it] that [the divorce document] fell from her and he found it.