Bhagavad Gita 4.40
अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति। नायं लोकोऽस्ति न परो न सुखं संशयात्मनः।।4.40।।
ajñaścāśraddadhānaśca saṃśayātmā vinaśyati| nāyaṃ loko'sti na paro na sukhaṃ saṃśayātmanaḥ||4.40||
ajnashcashraddadhanashca samshayatma vinashyati nayam loko'sti na paro na sukham samshayatmanah4.40
Meaning
The ignorant, the faithless, and the doubting soul perish. For the doubting person, there is neither this world, nor the next, nor happiness. Doubt is the greatest enemy of spiritual progress.
अज्ञानी तथा श्रद्धारहित और संशययुक्त पुरुष नष्ट हो जाता है, (उनमें भी) संशयी पुरुष के लिये न यह लोक है, न परलोक और न सुख।
This is verse 40 of 42 in Chapter 4 (Jnana Karma Sanyasa Yoga) of the Bhagavad Gita.