Bhagavad Gita 2.66

नास्ति बुद्धिरयुक्तस्य न चायुक्तस्य भावना।न चाभावयतः शान्तिरशान्तस्य कुतः सुखम्॥

nāsti buddhirayuktasya na cāyuktasya bhāvanā |na cābhāvayataḥ śāntiraśāntasya kutaḥ sukham ||

There is no knowledge of the Self for the unsteady, and no meditation is possible for the unsteady, and no peace for the unmeditative, and how can there be happiness for one who has no peace?

Right discrimination is not for him who cannot concentrate. Without concentration, there cannot be meditation; he who cannot meditate must not expect peace; and without peace, how can one expect happiness?

Our plain-language meaning of this verse is waiting for scholar review.