128 Kiddushin 4/1-4

(1) Ten [familial] statuses rose[came up] from Babylonia [to Israel]: Kohanim, Levites, Israelites, chalalim [offspring of a union prohibited to Kohanim, and who is thereby disqualified for the priesthood for marriage and Temple service.], proselytes, freed slaves, mamzerim [the offspring of certain prohibited relationships who may not marry into the general Jewish population], netinim [Gibeonites], shetukim and asufim. Kohanim, Levites and Israelites are permitted to [marry] with one another. Levites, Israelites, chalalim, proselytes, and are permitted to marry one another. Proselytes, freed slaves, mamzerim, netinim, shetukim and asufim are permitted to marry one another.

(2) And which are the shetukim? Anyone who knows [who] his mother [is], but does not know [who] his father [is]. And which are the asufim? Anyone who was gathered in from the market, and does not know [who] either his father or his mother [is]. Abba Shaul would call the shetukei, "investigated ones."

(3) All who are forbidden to marry within the [regular Jewish] community, are permitted to marry each other. Rabbi Yehudah forbids [this]. Rabbi Eliezer says, "[Those with] certain [status marrying others] with certain status is permitted; [those with] certain [status marrying others] with uncertain status, [those with] uncertain [status marrying others] with certain status, and [those with] uncertain [status marrying others] with uncertain status is [all] forbidden." And which are the uncertain ones? shetukim, asufim, and Samaritans.

(4) One who marries a Kohenet [the daughter of a kohen] needs to investigate her [status with regard to] four mothers, which are eight: Her mother; and her mother's mother; and her mother's father's mother, and her mother; and her father's mother, and her mother; and her father's father's mother, and her mother. [If a Kohen wants to marry] a Levite or an Israelite [woman], we add on to these another one.