Sefer Chasidim Siman 849
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
אדם שיש בידו אגוז אחד אל יברך ואחר כך ישבר האגוז. שמא התליע הגרעין או נרקב ונמצא שבירך לבטלה:
Medieval Jewish mysticism, translated by Sholom Alchanan Singer. Northbrook, Ill. Whitehall Co., 1971
One who has a nut in his hand should not recite a blessing on it before he splits it open for perhaps the nut is wormy or rotten inside and thus the blessing would be recited in vain.