Bhagavad Gita 12.5

क्लेशोऽधिक्तत्रस्तेषामव्यक्तासक्तचेतसाम् |
अव्यक्ता हि गतिर्दु:खं देहवद्भिरवाप्यते

Translation

For those whose minds are attached to the unmanifest, the path of realization is full of tribulations. Worship of the unmanifest is exceedingly difficult for embodied beings.