לרפואת אבי מורי שליט"א ר' יצחק יונה בן חנה בתוך שח"י

What is the din if a father says that he is SURE that his son was born during בין השמשות [and thus מספק he should have his bris on the eighth day from that night] while two עדים say that he was born before שקיעה [and the bris would be the previous day]. Does Beis Din take the child and give him his bris according to the testimony of the עדים or do we say שויא אנפשיה [and it is אסור according to the father to have the bris a day earlier] and the father does as he understands and circumcises later? 

Rav Bunim Eiger said that we don't say שויא to be מבטל a mitzva so that would mean that the Beis Din would do the bris a day earlier than the father would have it. With this he answered the question in the שו"ת רחש לבב [Siman י"ב, written by the son in law of R' Akiva Eiger, R' Chaim Shmuel Birnbaum who, incidentally, if I am not mistaken, was a chossid. As was the son in law of Rav Chaim Soloveitchik R' Hirsch Glickson. Two points for the Besht!!] on the gemara in Sanhedrin [44b] that when עדים testify that someone is חייב מיתה even though they retract we don't say שויא אנפשיה and it is as if their hand was cut off [if that happens the חיוב מיתה is off] and the חיוב מיתה is cancelled. Why DON'T we say שויא אנפשיה? According to their story he is no longer חייב מיתה?! The answer is that we don't say שויא אנפשיה to be מבטל an מצוה. 

There is a proof to this from the Mishna in Krisus [3-1] that if two people say that you ate חלב you have to bring a קרבן. Why is that? He claims that he didn't eat חלב and שויא אנפשיה that he can't bring a קרבן b/c it would be חולין בעזרה?? Again we see that we don't say שויא to be מבטל a מצוה. 

This principle also emerges from the Beis Yaakov [Ksubos 10a] that we force a מוציא שם רע to never divorce the girl. But according to him she is forbidden? Same יסוד - We don't say שויא to be מבטל a מצוה. 

[מאוצרות הגר"א גנחובסקי זצ"ל]