Sāriputta tells the monks of the qualities which lead to their deterioration not listening to the Dhamma, not having clear ideas about it, not practising it, and not obtaining fresh knowledge thereof. He who wishes to progress should train himself to know both his own mind and the minds of others; he should practise introspection. A.v.102 ff.
On eight conditions which lead to the degeneration of a learner, and their opposites. A.iv.331f.
On the six stations of mastery (cha abhibhāyatanāni) which prevent a monk from falling away. Seeing an object with the eye, he does not allow evil and unprofitable states to arise in his mind, memories and hopes akin to fetters that bind. Likewise with the other senses. S.iv.76f.
A conversation between Ananda and Bhadda at the Kukkutārāma in Pātaliputta, regarding decay and non decay. S.v.173.