Kidushin4: 3
כָּל הָאֲסוּרִים לָבֹא בַקָּהָל מֻתָּרִים לָבֹא זֶה בָזֶה; רַבִּי יְהוּדָה אוֹסֵר. רַבִּי אֱלִיעֶזֶר אוֹמֵר: וַדָּאָן בְּוַדָּאָן — מֻתָּר. וַדָּאָן בִּסְפֵקָן, וּסְפֵקָן בְּוַדָּאָן, וּסְפֵקָן בִּסְפֵקָן — אָסוּר. וְאֵלּוּ הֵן הַסְּפֵקוֹת: שְׁתוּקִי, אֲסוּפִי, וְכוּתִי.
All who are prohibited to enter into the Congregation are allowed to intermarry with each other; R’ Yehudah prohibits [it]. R’ Eliezer says: Those who are definite[ly unfit] with those who are definite[ly unfit] is permitted. Those who are definite[ly unfit] with those who[se status is doubtful, those who[se status] is doubtful with those who are definite[ly unfit], and those who[se status] is doubtful with those who[se status] is doubtful are prohibited. Those who[se status] is doubtful are: a shesuki, a foundling, and a Cuthean.