Reference for Pesachim 181:2

על כולם אין שוחטין עליהן בפני עצמן שמא יביאו את הפסח לידי פסול

[YET IN THE CASE OF] ALL THESE, ONE MAY NOT SLAUGHTER FOR THEM ALONE, LEST THEY BRING THE PASSOVER-OFFERING TO DISQUALIFICATION.<span class="x" onmousemove="('comment',' The omen may defile himself through the corpse; he who is removing the debris may find the person underneath it dead, in which case he himself is unclean; the prisoner may not be freed; while the invalid and aged person may grow weaker. Therefore they must be registered with others.');">³</span> THEREFORE IF A DISQUALIFICATION OCCURS TO THEM, THEY ARE EXEMPT FROM KEEPING THE SECOND PASSOVER,<span class="x" onmousemove="('comment',' Since they were actually fit when the animal was slaughtered.');">⁴</span>

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