וַיֹּ֣אמְרוּ לוֹ֩ אֱמָר־נָ֨א שִׁבֹּ֜לֶת וַיֹּ֣אמֶר סִבֹּ֗לֶת וְלֹ֤א יָכִין֙ לְדַבֵּ֣ר כֵּ֔ן וַיֹּאחֲז֣וּ אוֹת֔וֹ וַיִּשְׁחָט֖וּהוּ אֶל־מַעְבְּר֣וֹת הַיַּרְדֵּ֑ן וַיִּפֹּ֞ל בָּעֵ֤ת הַהִיא֙ מֵֽאֶפְרַ֔יִם אַרְבָּעִ֥ים וּשְׁנַ֖יִם אָֽלֶף׃
Então lhe diziam: "Dize, pois, 'Shibolet'." E ele dizia "Sibolet," pois não conseguia pronunciar corretamente. Então o agarravam e o matavam nas travessias do Yarden. E caíram naquele tempo de Efrayim quarenta e dois mil.
Mishneh Torah, Prayer and the Priestly Blessing
Six things prevent the performance of the rite of the Priestly Benediction: Defective speech; Physical blemishes; Transgressions; Wine; Age; Uncleanliness of the hands. Defective speech: Sufferers from a defect in speech, who cannot utter the letters as they should be pronounced, who, for example, read Aleph as if it were Ayin, or vice versa, or Shibboleth as if it were Sibboleth, etc., do not perform the rite of the Priestly Benediction. So too, those who are heavy of tongue and whose utterance is thick so that they are not understood by all, do not perform this rite.