Hiddur Mitzvah for a la'av - does it exist?

Question

One of the reasons given for people having long peyos is because there is a prohibition to cut them very short and they are beautifying the mitzvah by letting then grow really long. My thinking that this is a reason is mainly hearsay. https://judaism.stackexchange.com/a/37316/12837 says something quite similar. I quote today's OU halacha yomi:

In addition, Rav Belsky, zt”l felt that extending the length of the peyos beyond what is halachically required is a fulfillment of the concept of hidur mitzvah, beautification of the mitzvah. Just as there is hidur mitzvah by using aesthetically pleasing objects (such as a beautiful pair of tefillin or a beautiful esrog – see Shabbos 133b) so too there is a hidur mitzvah by sporting longer peyos, which demonstrate our pride in the mitzvah. This is evident from the fact that Jews throughout the centuries, living in many different countries, have grown longer peyos than are halachically mandated. (Shulchan HaLevi p. 124)

I think the following question stands whether or not that which I have said till now is true, but this was how the question came to mind.

The source of hiddur mitzvah is shabbos 133b which a list of things that you can make beautiful. They all refer to mitzvos asei. Is there a source (as early as possible) for the idea of beautifying a la'av?

In case you ask, the logic for distinguishing between an asei and a la'av is compelling. You are commanded to do something so you do it nicely. If you are commanded not to do something, you just don't do it... you don't 'not do it beautifully.'

Answer 1

First, a parallel to the idea behind the question: The Maharal in Gur Aryeh writes that the Avot fulfilled only positive mitzvot but not negative ones because there is no value in refraining from something without having been commanded. Another parallel may be the comment of Tosfot in Niddah (66b) that there is no preferred method to perform something which is not a mitzvah:

וי"ל דאין סברא גבי טבילה שלא הקפידה תורה אלא שיטהר האדם ואין לומר דלכתחילה לבעי דכיון דבדיעבד טהור לכתחלה נמי לא בעי ותעלה לו טבילה אבל בילה ומקרא בכורים וחליצה מצות נינהו הלכך לכתחלה ליעבד

With regard to this particular mitzvah, R. Yechezkel Rubin (Noam vol. 6, p. 320) suggests that there is no mitzvah of hiddur since it is a lo ta'aseh.

However, the concept of hiddur mitzvah in mitzvot lo ta'aseh is not unprecedented. The Bnei Yissaschar (Kislev/Tevet, no. 5) quotes the Rama mi-Pano to establish that hiddur mitzvah applies to mitzvot lo ta'aseh--because refraining can be a positive as well:

יש מהם שאפילו בהרחקת הלאוין יקרא עושה טוב לאסור בזיקים וכבלי ברזל המתעה בהן וצבאו ופקודיו תחת שלטנותא דקוב"ה

With regard to the specific mitzvah of לא תקיפו פאת ראשכם, R. Yosef Chaim of Baghdad in his Torah Lishmah (no. 389) writes that there is a hiddur mitzvah to leave one's payot longer than required:

והנה כאן צריך להחמיר להשאיר שיעור כדי לכוף ראשן לעיקרן וסגי בהכי כפי הדין מיהו ודאי אם יהיו יותר ארוכים עדיף טפי כדי שיהיו ניכרים יותר וזהו נוי שלנו שאנחנו מתנאים במצות השי"ת

This idea of hiddur for payot is cited as well in the name of the Chazon Ish. R. Tzvi Fromer (Eretz Tzvi, no. 3) claims that this is hiddur akin to that of eating additional matzah on the first night of Pesach--although not required, the additional matzah is also a mitzvah. However, R. Binyamin Zilber (Az Nidberu vol. 3, p. 92) argues that the two cases are not comparable, inasmuch as leaving hairs that are not part of the פיאות הראש is not part of the mitzvah.