Shavuos 20b - B'dibur Echad Ne'mru

The gemara says that the concept of זכור ושמור בדבור אחד נאמרו is a method of making woman obligated in the positive mitzvos of shabbos, just as they are obligated in the negative (sha'mor). Therefore the gemara says that woman are obligated m'doraysa in the mitzvah of kiddush, even though they are generally exempt from time bound mitzvos of that type. The gemara indicates that the mitzvah of kiddush is a mitzvah d'oraysa, but Tosafos qualifies this by saying that the mitzvah d'oraysa just requires verbally recognizing the kedushas hayom, or perhaps even requires saying the kedushas hayom over a cup of wine. The mefaresh in nazir learns the gemara there completely differently and understands that even the drinking the wine on which the kiddush was made is considered d'oraysa. Although rashi here quotes the drasha of זכרהו על היין, it isn't clear if his intent is to say that the wine is a required m'doraysa, or if rashi is just trying to show that the mitzvah of zachor refers to kiddush (but m'doraysa wouldn't require wine at all).

The Maharatz Chiyus quotes a teshuvas maharam alshiker quoting the ge'onim (rabbeinu hai) that whenever the expression of b'dibur echad is used, it means that that aseh creates a conflict with the lo ta'aseh and needed to be said b'dibur echad to remove the issur in case of conflict. The maharik (139) writes that the conflict created between the mitzvah of zachor and the mitzvah of shamor is that shamor forbids all chilul shabbos, but zachor demands violating for a choleh (although the gemara in yoma darshens - חלל שבת אחת כדי שישמרו שבתות הרבה from the term shamor, not zachor). In a situation of pikuach nefesh there is a conflict. Zachor says to violate so that shabbos will ulitmately be remembered and shamor says not to violate - but it was said b'dibur echad to teach that there is no issur under those circumstances. Based on this approach it should follow that the issur of shabbos is הותרה in cases of pikuach nefesh, not דחויה as the rambam writes in hilchos shabbos. It would also come out that only shabbos is hutra for pikuach nefesh, but other issurim are דחויה and not completely mutar because only within the issur of shabbos was this exemption made. From this it should follow that if one has a choice of violating shabbos or issur of eating treif food for pikuach nefesh, they should choose to violate shabbos since it is hutra not d'chuya. This would explain the opinion of Rabbeinu Meir (quoted in Rosh in Yoma 8:14) in a situation of pikuach nefesh when they were trying to decide whether to shecht on shabbos (violating shabbos) or eat ne'veila - Rabbeinu Meir says that violating shabbos for a choleh is like ochel nefesh on yom tov, which is completely mutar and therefore should be picked before the violation of neveila which is more in the category of d'chuya. Based on the concept of dibur echad, we understand where Rabbeinu Meir would be coming from.