These are all the references in the Dīgha Nikāya:
• The bhikkhunī Nandā passes away at Nadikā; the Buddha declares her an anāgāminī.
• The Buddha had told Māra in the past that he wouldn’t pass away until he had bhikkhus, bhikkhunīs, upāsakas and upāsikās who were “accomplished, trained, skilled, learned, knowers of the Dhamma, trained in conformity with the Dhamma … etc.” Māra visits the Buddha to remind him of this and point out that he does now have such disciples.
• “Whatever bhikkhu, bhikkhunī, upāsaka or upāsikā dwells practising the Dhamma properly, and perfectly fulfils the Dhamma-way, he or she honours the Tathāgata, reveres and esteems him and pays him the supreme homage.”
• The benefits of bhikkhus, bhikkhunīs, upāsakas and upāsikās visiting the four saṃvejanīyaṭṭhānas.
• Ānanda praised for knowing when it’s the right time for bhikkhus, bhikkhunīs, upāsakas and upāsikās to visit the Tathāgata.
• The second of Ānanda’s four remarkable and wonderful qualities is that when bhikkhunīs come to visit him they are “pleased at the sight of him, and when Ananda talks Dhamma to them they are pleased, and when he is silent they are disappointed.”
The Buddha relays to Ānanda the Brahmā Sanankumāra’s address to the Tāvatiṃsa devas. Ānanda then relays it to the bhikkhus, bhikkhunīs, upāsakas and upāsikās.
The discourse concludes with the Buddha telling Sāriputta that he should frequently tell bhikkhus, bhikkhunīs, upāsakas and upāsikās about its contents. “And any foolish people who have doubts or queries about the Tathāgata will, by listening to such talk, have their doubts and queries resolved.”
"But, Cunda, if the holy life is so circumstanced, and there is no teacher who is senior, of long standing, long-ordained, mature and advanced in seniority, then in such a case the holy life will be imperfect. But if such a teacher exists, then the holy life can be perfected in such a case.
“If in such a case there is such a senior teacher, but if there are no senior disciples among the bhikkhus, who are experienced, trained, skilled, who have attained peace from bondage, who are able to proclaim the true Dhamma, able to refute any opposing doctrines that may arise by means of the true Dhamma, and, having done so, give a grounded exposition of Dhamma, then the holy life is not perfected.”
The second paragraph is then repeated, replacing “senior bhikkhus” with middle-standing bhikkhus, junior bhikkhus, senior bhikkhunīs, middle-standing bhikkhunīs, junior bhikkhunīs, upāsakas and upāsikās.
Seven of the thirty-two marks of the mahāpurisa relate to features of his relationship with the four assemblies: bhikkhus, bhikkhunīs, upāsakas and upāsikās.
Taught so that bhikkhus, bhikkhunīs, upāsakas and upāsikās may dwell guarded, protected, unharmed and at ease.
The sixth of the nine inopportune times for living the brahmacariyā is being born in the border regions among foolish barbarians where there are no bhikkhus, bhikkhunīs, upāsakas or upāsikās.