On the authority of Abu Sa'id al-Khudri (may Allah be pleased with him), who said that the Messenger of Allah (PBUH) said:

Allah will say to the inhabitant of Paradise: O inhabitants of Paradise! They will say: O our Lord, we present ourselves and are at Your pleasure, and goodness rests in Your hands. Then He will say: Are you contented? And they will say: And how should we not be contented, O Lord, when You have given to us that which You have given to no one else of Your creation? Then He will say: Would not like Me to give you something better than that? And they will say: O Lord and what thing is better than that? And He will say: I shall cause My favour to descend upon you and thereafter shall never be displeased with you.

It was related by al-Bukhari (also by Muslim and at-Tirmidhi).