Liturgy for Niddah 122:2
אבדה בו שכבת זרע חדש בודקו במחט שחוק בודקו בחמה
If semen was lost in it, when new it should be examined with a needle,<span class="x" onmousemove="('comment',' Dried up semen offers some resistance to its penetration. ');"><sup>2</sup></span>
Seder Ma'amadot
Gemara (Niddah 61b:3)
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