Reference for Chullin 99:16

אמר רב כהנא

But what is this matter of 'Mourning' [concerning which the halachah is in accordance with the view of R'Simeon]? - It has been taught: In the first three days of mourning he who arrives from a place nearby counts the days of mourning with the others;<span class="x" onmousemove="('comment',' V. M.K. 21b. A man who was not more than a day's journey away from home when the death of a near relative occurred and who returned to his home within the first three days of the mourning, joins the other mourners in the counting of the Shib'ah, or the traditional seven days of mourning, and his period of mourning comes to an end at the same time as that of the others.');">⁸</span>

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