Reference for Shevuot 53:3

אמרו לו לא אם אמרת בשבועת הרשות שכן עשה בה לאו כהן תאמר בשבועת מצוה שלא עשה בה לאו כהן שאם נשבע לבטל ולא ביטל פטור:

But how do we know that the verses refer to optional matters, perhaps they refer [also] to matters relating to precepts? - That cannot enter our minds, for we require that doing good shall be similar to doing evil, and that doing evil shall be similar to doing good; for [the verse] likens doing evil to doing good: just as doing good cannot refer to the annulling of a precept, so doing evil

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow

Jastrow