釋禪波羅蜜次第法門 2.107

2.107

疑自者，若人作是念：「我諸根暗鈍，罪垢深重，非其器乎！」作此自疑，定法終不發也。欲去之者，無得自輕，以宿世善根難測故。

Doubt regarding oneself means that a person thinks: “My faculties are dull and obtuse, my karmic stains are deep and heavy; am I not an unfit vessel?” Entertaining this self-doubt, the dharma of concentration will never arise. If one wishes to eliminate it, one must not belittle oneself, because wholesome roots from past lives are difficult to measure.