As we learned in the Mishna (18b), when a signed document needs to be authenticated, under certain circumstances the original witnesses who are brought in are believed if they say: “anusim hayinu – we were coerced,” “ketanim hayinu – at the time we were minors” or“pesulim hayinu – we were disqualified witnesses.” Our Gemara presents a baraita in which Rabbi Meir disagrees with this ruling, and argues that even with these explanations, we can never allow witnesses to deny their original testimony.
Rav Ḥisda explains that Rabbi Meir disagrees about the pesulim hayinu argument because he holds that a person is not allowed to testify falsely, even if his life is being threatened. This explanation appears difficult to understand, since the general approach of all the Sages throughout the Talmud is that only three sins are so severe that they cannot be transgressed when someone’s life is at stake – Avoda Zara (idol worship), Gilui Arayot (forbidden sexual relations) and Shefikhut Damim (murder) – see Massekhet Pesahim 25.
The Ramban suggests that although a person is not obligated to risk his life for any mitzvah aside from these three, it would be considered a middat hasidut – an attribute of piety – to do so. Thus, a person who admits that he hadn’t done this righteous act is, on some level, admitting that he did not do all that he could have.
This question is the focus of a basic disagreement between the Rambam and Tosafot. According to the Rambam, it is forbidden for a person to give up their life for any mitzva aside from the three specific ones mentioned above. According to Tosafot, the Ramban and others, although no one is obligated to give up their lives rather than transgress other mitzvot, should they choose to do so it would be considered an attribute of piety.