Reference for Bekhorot 116:2

אי באחד באלול ר"ה דאלול ותשרי מצטרפין ודאב פטורים

and the rest are exempt in any case, for if the first of Elul is New Year [for cattle tithe], [the animals] of Elul and Tishri combine [to enter one shed] and those of Ab are exempt,<span class="x" onmousemove="('comment',' Because there are no more than five lambs belonging to that year.');">²</span>

Jastrow

Jastrow