Midrash for Kiddushin 4:1
עֲשָׂרָה יוֹחֲסִין עָלוּ מִבָּבֶל, כַּהֲנֵי, לְוִיֵּי, יִשְׂרְאֵלֵי, חֲלָלֵי, גֵּרֵי, וַחֲרוּרֵי, מַמְזֵרֵי, נְתִינֵי, שְׁתוּקֵי, וַאֲסוּפֵי. כַּהֲנֵי, לְוִיֵּי וְיִשְׂרְאֵלֵי, מֻתָּרִים לָבֹא זֶה בָזֶה. לְוִיֵּי, יִשְׂרְאֵלֵי, חֲלָלֵי, גֵּרֵי וַחֲרוּרֵי, מֻתָּרִים לָבֹא זֶה בָזֶה. גֵּרֵי וַחֲרוּרֵי, מַמְזֵרֵי וּנְתִינֵי שְׁתוּקֵי וַאֲסוּפֵי, כֻּלָּם מֻתָּרִין לָבֹא זֶה בָזֶה:
Ten degrees of pedigree went up from Bavel to Eretz Yisrael [Ezra separated all the p'sulin (those of defective pedigree) who were in Bavel, and brought them up with him, so that they not become intermixed with the pedigreed, no beth-din having been left in Bavel (to rule on such matters)]: Cohanim, Levites, Israelites, challalim [Cohanim born of those unfit for the priesthood, such as a widow to a high-priest, or a divorcée, a challalah, and a zonah to a regular priest], freed-men [freed bondsmen], mamzerim, Nethinim [Giveonites, who circumcised themselves in the days of Joshua and were forbidden to enter the congregation], shetukim and asufim [to be explained below]. Cohanim, Levites, and Israelites are permitted to intermarry. Levites, Israelites, proselytes, and freed-men are permitted to intermarry. Proselytes, freed-men, mamzerim, Nethinim, shetukim, and asufim — all are permitted to intermarry. [For the congregation of proselytes is not called a "congregation," and mamzerim were not exhorted against entering the congregation of proselytes. But Levites and Israelites may not marry mamzerim. And shetukim and asufim are possibly mamzerim and are permitted to intermarry with confirmed mamzerim. For we say that it is a confirmed "congregation" that he (the mamzer) may not enter, but not a possible one.]