Midras Imamat 27:32: Sifra, Mekhilta DeRabbi Yishmael & Midrash Tanchuma

1) "all that shall pass under the staff": to exclude a treifah (an animal with an organic defect), which does not pass. This tells me only of his counting them with the staff. If he did not count them with the staff, or if he counted them lying down or standing, whence do I derive (that it is valid)? From "shall be holy" (in any event). This tells me only of his calling it "the tenth." Whence do I derive (that it is valid) even if he did not call it "the tenth"? From "the tenth shall be holy." I might think that even if he had one hundred and took ten (at random), or ten and took one (that it is valid); it is, therefore, written "the tenth," and this is not ma'aser (lit., the tenth). R. Yossi b. R. Yehudah says: It is ma'aser.

2) Whence is it derived that if he (erroneously) called the ninth the tenth; the tenth, the ninth; and the eleventh, the tenth, that all three are considered (as ma'aser)? From "the tenth shall be holy to the L–rd." I might think to include the eighth and the twelfth (that he called the tenth). Would you? No. Since it is consecrated and its "error" is consecrated, just as only what is closest to it (i.e., it itself) is consecrated, so only the "error" closest to it (i.e., the ninth and the eleventh) is consecrated (and not the eighth and the twelfth).

3) In sum: If he called the ninth the tenth and the tenth the ninth and the eleventh the tenth, all three are consecrated. The ninth is eaten when it sustains a blemish, the tenth is ma'aser, and the eleventh is sacrificed as peace-offerings and makes a substitute. These are the words of R. Meir. R. Yehudah said: Can a substitute make a substitute? They said in the name of R. Meir: If it were a substitute, it would not be sacrificed. If he called the ninth the tenth, and the tenth the tenth, and the eleventh the tenth, the eleventh is not consecrated. If he called the ninth the tenth, and the tenth the eleventh, and the eleventh the tenth — Rebbi says that it (the eleventh) is not consecrated and R. Yossi b. R. Yehudah says that it is consecrated. This is the rule: R. Meir was wont to say: Whatever the name "the tenth" was not uprooted from, what comes before it is consecrated; what comes after it is not consecrated.