SN 29.1 Suddhika Sutta: Simple Version At Savatthi. "Bhikkhus, there are these four modes of generation of nagas. What four? Nagas born from eggs, nagas born from the womb, nagas born from moisture, nagas of spontaneous birth. These are the four modes of generation of nagas."
SN 29. 2 Paṇītatara Sutta: Superior At Savatthi. "Bhikkhus, there are these four modes of generation of nagas .... "Therein, bhikkhus, nagas born from the womb, from moisture, and born spontaneously are superior to nagas born from eggs. Nagas born from moisture and born spontaneously are superior to nagas born from eggs and from the womb. Nagas born spontaneously are superior to nagas born from eggs, from the womb, and from moisture. These, bhikkhus, are the four modes of generation of nagas."
(Dragons may be born from eggs, the womb, moisture, or spontaneously. Those born spontaneously are the best.)
SN 29.3 Uposatha Sutta: The Uposatha (1)
At Savatthi. Then a certain bhikkhu approached the Blessed One, paid homage to him, sat down to one side, and said to him: "Venerable sir, what is the cause and reason why some egg-born nagas here observe the Uposatha and relinquish [concern for] their bodies?"
"Here, bhikkhus, some egg-born nagas think thus: 'In the past we acted ambivalently in body, speech, and mind. Having done so, with the breakup of the body, after death, we were reborn in the company of egg-born nagas. If today we praise good conduct of body, speech, and mind, then with the breakup of the body, after death, we shall be reborn in a happy destination, in a heavenly world. Come now, let us practice good conduct of body, speech, and mind.' "
"This, bhikkhu, is the cause and reason why some egg-born nagas here observe the Uposatha and relinquish [concern for] their bodies." (Egg born dragons sometimes transform their bodies and observe the sabbath in order to get a good rebirth.)
SN 29.4-6 The Uposatha (2-4)
(The same is repeated for the other three types of nagas.)
(Egg born, womb born, moisture born and spontaneously born dragons sometimes transform their bodies and observe the sabbath in order to get a good rebirth.)
SN 29.7 Suta Sutta: He Has Heard (1)
At Savatthi . . .. Sitting to one side, that bhikkhu said to the Blessed One: "Venerable sir, what is the cause and reason why someone here, with the breakup of the body, after death, is reborn in the company of egg-born nagas?"
"Here, bhikkhu, someone acts ambivalently in body, speech, and mind. He has heard: 'Egg-born nagas are long-lived, beautiful, and abound in happiness.' He thinks: 'Oh, with the breakup of the body, after death, may I be reborn in the company of eggborn nagas!' Then, with the breakup of the body, after death, he is reborn in the company of egg-born nagas. "
"This, bhikkhus, is the cause and reason why someone here, with the breakup of the body, after death, is reborn in the company of egg-born nagas."
(One becomes an egg born dragon due to ambivalent deeds in a past life and the appropriate aspiration.)
SN 29.8-10 He Has Heard (2-4)
(These three suttas repeat the same for the other three types of nagas.)
(One becomes a womb born/moisture born/spontaneously born dragon due to ambivalent deeds in a past life and the appropriate aspiration.)
SN 29.11-20 Aṇḍajadānūpakārasuttadasaka: With the Support of Giving (1)
Sitting to one side, that bhikkhu said to the Blessed One: "Venerable sir, what is the cause and reason why someone here, with the breakup of the body, after death, is reborn in the company of egg-born nagas?"
"Here, bhikkhu, someone acts ambivalently in body, speech, and mind. He has heard: 'Egg-born nagas are long-lived, beautiful, and abound in happiness.' He thinks: 'Oh, with the breakup of the body, after death, may I be reborn in the company of egg-born nagas!' He gives food ... . He gives drink .... He gives clothing .... He gives a vehicle ... . He gives a garland .... He gives a fragrance .... He gives an unguent ... . He gives a bed .... He gives a dwelling .... He gives a lamp. Then, with the breakup of the body, after death, he is reborn in the company of egg-born nagas. "
"This, bhikkhus, is the cause and reason why someone here, with the breakup of the body, after death, is reborn in the company of egg-born nagas."
(One becomes an egg born dragon due to ambivalent deeds in a past life, the appropriate aspiration, and giving various gifts.)
SN 29.21-50 Jalābujādidānūpakārasuttattiṃsaka: With the Support of Giving (2-4)
(These three decads each repeat the preceding decad jar the other three types of nagas.)
(One becomes a womb born, moisture born, or spontaneously born dragon due to ambivalent deeds in a past life, the appropriate aspiration, and giving various gifts)
References 1. www.accesstoinsight.org 2. https://suttacentral.net/ 3. The connected discourses of the Buddha (Bhikkhu Bodhi)