Here are some passages from the Sutta-piṭaka
Katamañca, bhikkhave, amataṃ? Yo, bhikkhave, rāgakkhayo dosakkhayo mohakkhayo – idaṃ vuccati, bhikkhave, amataṃ. (SN iv 369)
'And what, bhikkhus, is the Deathless? The destruction of lust, the destruction of hatred, the destruction of delusion: this is called the Deathless'.
Evaṃ vutte so bhikkhu bhagavantaṃ etadavoca – ‘‘‘amataṃ, amata’nti, bhante, vuccati. Katamaṃ nu kho, bhante, amataṃ, katamo amatagāmimaggo’’ti? ‘‘Yo kho, bhikkhu, rāgakkhayo dosakkhayo mohakkhayo – idaṃ vuccati amataṃ. (SN v 8)
'Venerable sir, it is said, "the Deathless, the Deathless". What now, venerable sir, is the Deathless? What is the path leading to the Deathless?'
'The destruction of lust, the destruction of hatred, the destruction of delusion: this is called the Deathless'.
Etaṃ amataṃ yadidaṃ anupādā cittassa vimokkho. (MN ii 265)
This is the Deathless, namely release of mind through lack of clinging.
Khayaṃ virāgaṃ amataṃ paṇītaṃ, yadajjhagā sakyamunī samāhito;
Na tena dhammena samatthi kiñci, idampi dhamme ratanaṃ paṇītaṃ;
Etena saccena suvatthi hotu. (Khp 4)
The exquisite Deathless — ending, dispassion — discovered by the Sakyan Sage in concentration: There is nothing to equal that Dhamma. This, too, is an exquisite treasure in the Dhamma. By this truth may there be well-being.
‘‘Rūpadhātuṃ [rūpadhātu (sabbattha)] pariññāya, arūpesu asaṇṭhitā;
Nirodhe ye vimuccanti, te janā maccuhāyino.
‘‘Kāyena amataṃ dhātuṃ, phusayitvā [phussayitvā (syā.), phassayitvā (pī.)] nirūpadhiṃ;
Upadhippaṭinissaggaṃ, sacchikatvā anāsavo;
Deseti sammāsambuddho, asokaṃ virajaṃ pada’’nti. (Iti 45)
Comprehending the property of form, not taking a stance in the formless, those released in cessation are people who've left death behind.
Having touched with his body the deathless property free from acquisitions, having realized the relinquishing of acquisitions, fermentation-free, the Rightly Self-awakened One teaches the state with no sorrow, no dust.
‘‘Hitvā mamattaṃ manujesu brahme,
Nirāmagandho virato methunasmā,
Etthaṭṭhito ettha ca sikkhamāno;
Pappoti macco amataṃ brahmaloka’’nti. (DN ii 241)
'That man who spurns all possessive thoughts,
Alone, intent, compassion-filled,
Aloof from stench, free from lust –
Established thus, and training thus,
Can mortals reach the deathless Brahmā world'.
Bhagavaṃmūlakā no, bhante, dhammā...