Hindu Scriptures on Everlasting happiness

The person who is intelligent and wise and who knows what defects lie hidden in the objects [of enjoyment], knows how to free himself from the bonds of desire. Only such a person is fit to tread the path that leads to liberation. (Sarva-Vedanta-Siddhanta-Sarasangraha, 61)

The intelligent man gives up happiness and sorrow by developing concentration of mind on the Atman and thereby meditating on the ancient Deity who is inscrutable, lodged inaccessibly, located in the intellect, and seated in the midst of heart. (Katha Upanishad, 1.2.12)

Everlasting happiness is for those, and not for others, who are wise and realize as seated in their intellect him who is one and independent, who makes diverse the single seed of the many actionless (beings). (Shvetashvatara Upanishad, 6.12)