Is there any reference regarding this in any Veda or other books?
Who are Chiranjivis?
अश्वत्थामा बलिव्र्यासो हनूमांश्च विभीषण:। कृप: परशुरामश्च सप्तएतै चिरजीविन:॥ सप्तैतान् संस्मरेन्नित्यं मार्कण्डेयमथाष्टमम्। जीवेद्वर्षशतं सोपि सर्वव्याधिविवर्जित॥
8 Chiranjivis (immortals) are : Ashwatthama, King Bali, Krishna Dvaipāyana (Vedvayasa of 28th Dwapara Yuga), Hanuman, Vibhishan, Kripacharya, Parashurama and Markandaya.
Note: This list is highly disputed. Few sources only consider 7 Chiranjivis and few consider others as well (like Kak Bhusundi).
Ashwatthama, Krishna Dvaipāyana, Kripacharya and Parashurama
Will become one of the Saptrishis in 8th Manvantara. - Vishnu Purana
Note: Ashwatthama is also mentioned as Ved Vayasa in 29th Dwapara Yuga as well (Source). And Parashurama is Lord Vishnu's incarnation.
Will hold the title of Indra (yes Indra is a post) in 8th Manavantara by the grace of Lord Vishnu. - Vishnu Purana
Hanumana and Vibhishan
Will be living on earth till Lord Rama's history remains current. - Valmiki Ramayana: Uttarakhand