Source of the term בכתמים שומעין להקל

Question

In the halachos of Niddah, there is a term which I have come across not infrequently. The term is בכתמים שומעין להקל, which roughly translated means "in [the halachos of blood] stains we listen to the leniencies." The term seems to refer to a halachic principle that in these halachos we are more willing to be lenient like a minority opinion or an opinion which is not usually given such halachic weight. I first encountered this term in the Shach, then saw it in the Rema, and subsequently saw it in the Rosh. This is not a term which I have come across, as of yet, in any earlier source.

A search of Shas showed that the term does not appear in this form (H/T Shokhet). I am wondering where this term originates, and being that it is not from the Talmud, how the concept came to be accepted.

Answer 1

The Rosh in Niddah ch. 8 siman 8 writes the following:

דבדרבמן הולך אחר המיקל וכל שכן בכתמים

In Rabbinical rules we follow the lenient opinion, and certainly by kesamim.

The Divrei Chamudos אות צ there sources this comment to the last line of the previous Siman of the Rosh, in which the Rosh quoted the following:

כל שיעורי חכמים להחמיר חוץ מכגריס של כתמים

On all Rabbinical measurements we are stringent except for kesamim.

This is a quote from Niddah 58b.

The Divrei Chamudos asserts that from there the Rosh extrapolated to all laws of kesamim.

This doesn't source the origin of the term in the question, but it at least provides a Talmudic source for the concept that kesamim are treated more leniently. The Rosh in Siman 8 is applying this principle to the resolution of a dispute - i.e. he is deciding whose opinion to follow based on the rule that kesamim are more lenient.

Answer 2

Mishnah, Nida 58b--

מעשה באשה אחת שבאת לפני ר"ע אמרה לו ראיתי כתם אמר לה שמא מכה היתה ביך אמרה לו הן וחיתה אמר לה שמא יכולה להגלע ולהוציא דם אמרה לו הן וטהרה ר"ע ראה תלמידיו מסתכלין זה בזה אמר להם מה הדבר קשה בעיניכם שלא אמרו חכמים הדבר להחמיר אלא להקל שנאמר (ויקרא טו) ואשה כי תהיה זבה דם יהיה זובה בבשרה דם ולא כתם

Answer 3

I believe the term is based on .גמרא נדה נט where the גמרא discusses being strict / lenient with כתמים which are דרבנן.

אמר רבינא לא להקל על דברי תורה אלא להחמיר על דברי תורה וכתמים עצמן דרבנן

See רש"י there who elaborates further.

Another גמרא has a closer expression: :נידה סא

לא הותרו בגדי צבעונין לאשה אלא להקל על כתמיהן