Brihat Parashara Hora Shastra
विंशाधिकश्तं दीर्घे दिव्ये वर्षसहस्रकम् । तदूर्ध्वममितं पुण्यैरमितैराप्यते जनैः ॥ ५४॥
Super-natural life-span is 1000 years. Above this super-natural life-span of 1000 years it is Amritayu, which can be acquired only by those, who deserve it.
english translation
viMzAdhikaztaM dIrghe divye varSasahasrakam । tadUrdhvamamitaM puNyairamitairApyate janaiH ॥ 54॥
hk transliteration by Sanscript