Reference for Rosh Hashanah 14:5

ואימא תשרי סתם כי אגר איניש ביתא לכולהו ימות הגשמים אגר

And even according to those who say that one day in the year is reckoned as a year, this does not apply here, because a man would not trouble to rent a house for less than thirty days. But why should I not say that Tishri [is the New Year for letting houses]?<span class="x" onmousemove="('comment',' So that, if a man rents a house on the first of Elul for a year, he takes it only to the first of Tishri.');">⁵</span>

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