Happiness and rejoicing in the Heaven
The inhabitants of the Heaven will be always happy. The verses of the Koran confirm existence of rejoicing in the Paradise:
1- Some faces will be beaming on that day;
Laughing, rejoicing(80:38-39)
2-Some day you will believing men and believing women with their right steaming on ahead of them and off to their right : “your good news today [consists of] gardens through which rivers flow, to live in forever !” that will be the splendid Achievement . (57:12)
3- The ones who say: “ our Lord is God [Alone], then keep straight on ahead , will have angels alight on them [saying]: “Do not fear nor feel saddened and rejoice in word the Garden which you have been promised!
We are your sponsors during worldly life and in the Hereafter , during it you shall have whatever you souls may crave you will have whatever you request in it as hospitality from Someone [who is] forgiving, merciful”! (41:30-32)
4- Other faces will be blissful on that day,
Pleases with their effort,
(dwelling) in a lofty garden (88:8-10)
5-You will recognize a blissful splendor on their faces .(83:24)
6-O Tranquil soul, return to your Lord well pleased and pleasing [Him] ! Enter among My servants, and enter My garden.(89:27-30)
7-Some faces will be radiant on that day, looking toward their Lord.(75:22-23)
Sources :
al-Mizan Koranic exegesis (Allameh Tabatabai)
The Noble Quran (English translation by T.B. Irving)