大般涅槃經集解 60.34

60.34

案僧亮曰：不宜修定者，是人根鈍，煩惱勢盛、自疑犯戒，皆由著定，所以宜修空慧也。

Sengliang states: That 'it is not suitable to cultivate concentration' means that this person's faculties are dull, the power of his afflictions is rampant, and he doubts himself concerning transgressing precepts; these all stem from attachment to concentration, which is why it is suitable to cultivate emptiness and wisdom.