All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Trade is based on profit and loss, and the stock market is included in this. However, a Muslim should be sagacious and he should seek the advice of his Muslim brothers and benefit from the experiences of those who work in trade amongst them, so that they would advise him about some fields of investment that are safer and of less risk than the stock market. It is known that investing in it is the least safe field of investment these days.
Therefore, if this person wants to continue working in trade, he should look for another field. Allaah did not put His slaves in difficulty with regard to lawful trade; Allaah Says (what means): {But Allaah has permitted trade and has forbidden interest.}[Quran 2:275]
However, a Muslim should, first of all, beware of dealing with forbidden shares or lawful shares whose transactions take place in an unlawful manner as this is one of the reasons that incur the wrath of Allaah and eradicate the blessing, and incur loss; for more benefit, please refer to Fataawa 81504 and 85042.
On the other hand, this brother should be advised not to get many loans without a necessity, as he will be held responsible about them. It is appropriate to mention here some texts that show the seriousness of the loan. It is confirmed that the Prophet said: "The soul of a believer remains hanging with his debt till it is paid off.” [Ahmad, Abu Daawood, At-Tirmithi, An-Nasaa’i and Ibn Maajah] Moreover, the Prophet said: "Every sin of the martyr is forgiven except debt..” [Muslim]
Moreover, Jaabir narrated: “A man died and we washed him, perfumed him and enshrouded him, and then we brought him to the Prophet so that he would perform the funeral prayer on him. We said: “Would you perform the funeral prayer on him? He took a few steps and then he asked: “Does he have any debts?” We replied: “Yes, he has a debt of two dinars.” Upon hearing that, the Prophet went away. Then Abu Qataadah undertook to pay the debt. We, thereafter, went to the Prophet and Abu Qataadah told him, ‘I would pay the two dinars’. Then the Prophet said: “Will the creditor’s right be guaranteed and will the dead person be acquitted from debt?.” Abu Qataadah said: “Yes.” So, the Prophet performed the funeral prayer on him. After one day, the Prophet asked: “What was done about the two dinars.” Abu Qataadah replied: “He only died yesterday.” So, the second day, the Prophet asked him again the same question. Then, Abu Qataadah said: “I have paid them off.” Then, the Prophet said: ''It is only now that his skin has become cool.” [Ahmad]
Allaah Knows best.