Cetokhilasutta 6.2

6.2

Yo so, bhikkhave, bhikkhu sikkhāya kaṅkhati vicikicchati nādhimuccati na sampasīdati, tassa cittaṃ na namati ātappāya anuyogāya sātaccāya padhānāya.

'And further, O Bhikkhus, when a brother has doubt in the System of Self-culture (Sikkhâ), is uncertain about it, has no confidence in it, has no faith in it; then is his mind not inclined towards zeal, exertion, perseverance, and struggle.
'But whosesoever mind inclineth not towards zeal, exertion, perseverance, and struggle, he has not become free from this fourth spiritual barrenness.