Reference for Berakhot 12:4

יבטח בשם ה' מאי טעמא משום דהוה ליה לבטוח בשם ה' ולא בטח:

"Let him trust in the name of the Lord" (ibid.). For what reason [is the light denied him] ? Because he should have trusted in the name of the Lord, but did not.

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