Another source:
See Ba’ak Haturim (Devorim 25 12) “Loi Yihyeh lecho bekischo” one shouldn’t count what is in ones pocket because of ein habrocho motzui elo bedovot hasomui min huayin.
Another source:
See Sifsei Kohein al Hatoiro (Bamidbor 6 23) “Ko sevorchu es bnei Yisroel” a Yisroel says first the words of the psukim, then the kohen repeats them, however the brocho really comes from HKB”H. HKB”H doesn’t want the 60 SORIM ELYOINIM to be mekatreig on the brocho, therefore it is said in a somui (hidden) way – “ein habrocho motzui elo bedovot hasomui min huayin”.
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