Bhagavad Gita · 4.40

अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति।नायं लोकोऽस्ति न परो न सुखं संशयात्मनः॥

ajñaśh chāśhraddadhānaśh cha saṁśhayātmā vinaśhyati nāyaṁ loko 'sti na paro na sukhaṁ saṁśhayātmanaḥ

The ignorant, the faithless, and the doubting soul perishes. For the one who is full of doubt, there is neither this world, nor the next, nor any happiness.

— Bhagavad Gita 4.40

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)