http://www.fatwa-online.com/attaining-genuine-happiness/

Reference: Fataawa Noor ‘alad-Darb – Question No.6198, Page 22, Volume 12

Question: What is the appropriate treatment for [attaining] happiness, since I am living in extreme sadness; [please] guide me, and may you be rewarded?

Response: The appropriate treatment [for attaining genuine happiness] is to increase in the remembrance of Allaah (‘Azza wa Jall), [as] Allaah (Ta’aala) says:

{Unquestionably, by the remembrance of Allaah hearts are assured}, soorah ar-Ra’d, aayah 28

And from the [recommended] treatment is not to concern himself with the affairs of this world, and nor to overly concern himself with anything other than the Hereafter.

And [additionally], from the [recommended] treatment is that he spends on good causes, whether he spends [from his] wealth, or donates possessions, or physically exerts himself to help his brothers [and sisters in Islaam], or strives [in the name of Allaah] with his life – and [in shaa.-Allaah, the result of] all of this [will] lead to [genuine] happiness.

And he should also oft-recite this supplication:

‎{رَبِّ اشْرَحْ لِي صَدْرِي وَ يَسِّرْ لِي أَمْرِي}
{My Lord, expand for me my breast [with assurance], and ease for me my task}, soorah TaaHaa, aayahs 25-26