What is the real cause of this sadness? A person should turn to his Lord and seek Refuge in Him. He should supplicate with this supplication,
(قَالَ رَبِّ ٱشْرَحْ لِى صَدْرِى ٢٥ وَيَسِّرْ لِىٓ أَمْرِى)
“He said, "My Lord, expand for me my breast with assurance, and ease for me my task” (Ttaahaa 25-26)
and seek forgiveness,
“For whoever adheres to seeking Forgiveness, Allaah will make a source of relief out for him from every tight spot and from every sadness.” (Abu Daawood 1518)
Also a person should increase in the Remembrance of Allaah because,
(أَلَا بِذِكْرِ ٱللَّهِ تَطْمَئِنُّ ٱلْقُلُوبُ)
“Indeed, in the Remembrance of Allaah do heart find peace.” (AR-Ra’d 28)
The greatest form of Remembrance is the reciting of the Qur'aan in the manner we have been instructed, with reflection and slow and measured recitation. In this way, the chest will ease, and worry and grief will depart. If this sadness has another cause, then try to remove that cause also, whether it is a debt or other issues that we have in our lives. You must strive to remove this cause and seek Refuge in Allaah to help remove it.