“He who is a true believer liveth both in this world and in the world to come.”

"Know then that “life” hath a twofold meaning. The first pertaineth to the appearance of man in an elemental body, and is as manifest to thine eminence and to others as the midday sun. This life cometh to an end with physical death, which is a God-ordained and inescapable reality. That life, however, which is mentioned in the Books of the Prophets and the Chosen Ones of God is the life of knowledge; that is to say, the servant’s recognition of the sign of the splendours wherewith He Who is the Source of all
splendour hath Himself invested him, and his certitude of attaining unto the presence of God through the Manifestations of His Cause. This is that blessed and everlasting life that perisheth not: whosoever is quickened thereby shall never die, but will endure as long as His Lord and Creator will endure.

The first life, which pertaineth to the elemental body, will come to an end, as hath been revealed by God: “Every soul shall taste of death.” 14 But the second life, which ariseth from the knowledge of God, knoweth no death, as hath been revealed aforetime: “Him will We surely quicken to a blessed life.” 15 And in another passage concerning the martyrs: “Nay, they are alive and sustained by their Lord.” 16 And from the Traditions: “He who is a true believer liveth both in this world and in the world to come.” 17 Numerous examples of similar words are to be found in the Books of God and of the Embodiments of His justice. For the sake of brevity, however, We have contented Ourself with the above passages."

-Bahá'u'lláh, Gems of Divine Mysteries (Javáhiru’l-Asrár), pp. 47-48

14. Qur’án 3:185.
15. Qur’án 16:97. 
16. Qur’án 3:169. 
17. From a Hadíth.