”Why would you do something to be yotzei a safek if you don’t have to.(There’s a famous Reb Chaim which postulates that the rule of safek d’oraisa l’chumra would not apply in this type of situation”
Well being that nobody knows the source of this ”reb chaim” and the gemara and all the achronim are mevuar farkert than lhalacha we follow the psak of the mishna berura that safek deoraysa applies here.
The gemara in rosh hashana 34b ???? ??? ?????? ???? ?????? ????? ?????? ?????? ????? ??????? ???? ?????? ????? ??????? ????? ?? ???????? ?? ????? ?? ????? ??? ?? ?? ??? ???? ??? ??? and this is brought down lhalacha in siman ???’? and the mishna berura is clear the reason is because of safek deoraysa lchumra.
Also see the ran in succah 22b ?”? ???
and the mishna berura in Siman 32:50, 33:5 in Biur halacha ?”? ??? and MB 39:26 and Biur halacha in 648 ?”? ????? (page 136)
???? ???? ???. ???????? ???? ????? ?? ???? ???? ??? ????? ????”? ??????? ????”? ???? ?? .