釋禪波羅蜜次第法門 2.111

2.111

復次，佛法之中，信為能入；若無信者，雖在佛法，終無所獲。如是等種種因緣覺知疑過，當急棄之。

Furthermore, within the Buddha-Dharma, faith is that which enables entry; if one lacks faith, even though one is within the Buddha-Dharma, one will ultimately gain nothing. Aware of the faults of doubt through various such causes and conditions, one must promptly discard it.