Related על בבא מציעא 207:6

Hillel the Elder would explain lay-language [of contracts as if it were the biblical text]. When the people of Alexandria would betroth wives, another would come and seize her from the street. The matter came to the Sages. They sought to make their children bastards [since the betrothal was valid, so when they are married to others in the meantime their children will be illegitimate]. Hillel the Elder said to them: "Bring to me the ketubah of your mothers." They brought them for him, and it was written in it "When you enter my house, you will be my wife according to the law of Moshe and Yisrael" [in other words, based on a fine reading of the ketubah text, the betrothal only takes full effect when she enters his house, which means that the other husband was not illegitimate and her children aren't bastards].