Talmud for Rosh Hashanah 66:14
ואין לי אלא ביובל בראש השנה מנין ת"ל בחדש השביעי
I know this so far only of the Jubilee; how do I know it of New Year? The text says significantly, In the seventh month,<span class="x" onmousemove="('comment',' Ibid.');"><sup>26</sup></span> when there is no real occasion for the expression, in the seventh month.<span class="x" onmousemove="('comment',' Because it says immediately after, 'on the day of atonement'.');"><sup>27</sup></span> Why then does it say, in the seventh month? To show that all the teru'ahs of the seventh month should be of the same character. How do we know that there must be a plain blast<span class="x" onmousemove="('comment',' I.e., a teki'ah.');"><sup>28</sup></span> before it? Because it says, Thou, shalt make proclamation with a shofar of teru'ah.<span class="x" onmousemove="('comment',' Which is taken to mean 'shofar (i.e., teki'ah) and teru'ah'.');"><sup>29</sup></span> How do we know that there must be a plain blast<span class="x" onmousemove="('comment',' I.e., a teki'ah.');"><sup>30</sup></span> after it? Because it says, Ye shall make proclamation with the shofar.<span class="x" onmousemove="('comment',' Lev. XXV, 9. The repetition of the word shofar points to another teki'ah.');"><sup>31</sup></span> I know this only of the Jubilee; how do I learn it of New Year also? It says significantly, in the seventh month<span class="x" onmousemove="('comment',' Ibid.');"><sup>32</sup></span>