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