Commentary for Kiddushin 142:6
וכי תימא עובד כוכבים ועבד הבא על בת ישראל הולד כשר ודילמא מהנך דכתיב בהו (עמוס ו, ד) השוכבים על מטות שן וסרוחים על ערסותם ואמר רבי יוסי בר' חנינא אלו בני אדם המשתינים מים בפני מטותיהם ערומים
'Do we know whence we are descended? ' he retorted.' Perhaps from those of whom it is written: They ravished the women in Zion, the maidens in the cities of Judah.<span class="x" onmousemove="('comment',' Lam. V, 11.');"><sup>8</sup></span> And should you answer: If a heathen or slave has intercourse with the daughter of an Israelite, the issue is fit, - then perhaps [we are descended] from those of whom it is written, that lie upon beds of ivory, and stretch themselves [seruhim] upon their couches.<span class="x" onmousemove="('comment',' Amos VI, 4.');"><sup>9</sup></span>
Daf Shevui to Kiddushin
Daf Shevui to Kiddushin
In short, Ulla questions how R. Yehudah can be so sure about his lineage.