Dhp 182 Erakapattanāgarājavatthu
The Rare Things
A monk in the time of Buddha Kassapa dies and is reborn as a nāga. Eventually he hears that a new Buddha has arisen in the world, and goes and asks why he cannot attain rebirth as a human even after so long a time. This is the Buddha’s reply.
70. Kiccho manussapaṭilābho, kicchaṁ maccāna’ jīvitaṁ,
Kicchaṁ Saddhammasavanaṁ, kiccho Buddhānam-uppādo.
It is rare to be born human,
Rare is the life of a mortal,
It is rare to hear the Dhamma,
Rare the arising of Buddhas.