Bhagavad Gita 2.66
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?
नास्ति बुद्धिरयुक्तस्य न चायुक्तस्य भावना।
न चाभावयतः शान्तिरशान्तस्य कुतः सुखम्॥nāsti buddhirayuktasya na cāyuktasya bhāvanā|
na cābhāvayataḥ śāntiraśāntasya kutaḥ sukham||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).