Sangitisutta 2.1.78

2.1.78

Yo so, āvuso, bhikkhu satthari kaṅkhati vicikicchati nādhimuccati na sampasīdati, tassa cittaṃ na namati ātappāya anuyogāya sātaccāya padhānāya, yassa cittaṃ na namati ātappāya anuyogāya sātaccāya padhānāya, ayaṃ paṭhamo cetokhilo.

This being so, their mind doesn’t incline toward keenness, commitment, persistence, and striving. This is the first kind of hard-heartedness.