Ananda explains to Sariputta how to hear new Dhamma, and how not to get Dhammas mixed up:
Āyasmā ānando etadavoca —
“Idhāvuso sāriputta, bhikkhu dhammaṃ pariyāpuṇāti — suttaṃ geyyaṃ veyyākaraṇaṃ gāthaṃ udānaṃ itivuttakaṃ jātakaṃ abbhutadhammaṃ vedallaṃ. So yathāsutaṃ yathāpariyattaṃ dhammaṃ vitthārena paresaṃ deseti, yathāsutaṃ yathāpariyattaṃ dhammaṃ vitthārena paresaṃ vāceti, yathāsutaṃ yathāpariyattaṃ dhammaṃ vitthārena sajjhāyaṃ karoti, yathāsutaṃ yathāpariyattaṃ dhammaṃ cetasā anuvitakketi anuvicāreti manasānupekkhati. Yasmiṃ āvāse therā bhikkhū viharanti bahussutā āgatāgamā dhammadharā vinayadharā mātikādharā tasmiṃ āvāse vassaṃ upeti. Te kālena kālaṃ upasaṅkamitvā paripucchati paripañhati — ‘Idaṃ, bhante, kathaṃ; imassa kvattho’ti? Te tassa āyasmato avivaṭañceva vivaranti, anuttānīkatañca uttānīkaronti, anekavihitesu ca kaṅkhāṭhāniyesu dhammesu kaṅkhaṃ paṭivinodenti. Ettāvatā kho, āvuso sāriputta, bhikkhu assutañceva dhammaṃ suṇāti, sutā cassa dhammā na sammosaṃ gacchanti, ye cassa dhammā pubbe cetasā samphuṭṭhapubbā te ca samudācaranti, aviññātañca vijānātī”ti.
This is what Ananda said: “Sariputta, there’s the case in which a bhikkhu masters the Dhamma – suttas, mixed prose and verse, commentaries, verses, exclamations, discourses, birth stories, miracle stories, question-and-answer dialogues. Regarding what is heard and what is known, the bhikkhu explains the Dhamma in great detail; regarding what is heard and what is known, the bhikkhu recites the Dhamma in great detail; regarding what is heard and what is known, the bhikkhu thoroughly studies the Dhamma, regarding what is heard and what is known, the bhikkhus aims to reflect on, and think about the Dhamma, and consider it carefully. He spend the rains retreats wherever senior bhikkhus dwell, learned knowers of the suttas, experts in the Dhamma, the Vinaya and the Patimokkha. When you approach this bhikkhus at an appropriate time and ask: ‘What is the reason for this, Bhante, why is it like that?’ that venerable one makes it clear, reveals the truth, explains deeply; faced with various reasons and causes for doubting the Dhamma, he dispels doubt. In such a case, friend Sariputta, a bhikkhu can hear Dhamma he has not heard before, and not get confused by Dhammas, and remember the Dhamma he has touched in the past, and understand what he has not known before.”
Ananda Sutta, AN 6.51