A morsel of halaal food

Eating haraam gives rise to every type of infamy. Whereas, the halaal morsel is the cause of every kind of goodness and charity. Numerous traditions praise the acquisition of livelihood through lawful means. For example the Holy Prophet (s.a.w.s.) says, 
"Worship consists of seventy parts and the best part is earnings by lawful means." 
(Safinatul Behaar)

The Messenger of Allah has also said, 
"When a man eats halaal food an angel stands over his head and prays for his forgiveness till he finishes eating." 
(Safinatul Behaar)

The Prophet has remarked in a similar vein, 
"One who strives to earn his livelihood in a lawful manner from morning till night, achieves salvation." 
(Safinatul Behaar)

The Holy Prophet (s.a.w.s.) states that Allah has said: 
"I will not care on the Day of Qiyamat from which door he enters Hell, the person who does not care from which door he earns money in this world." 
(Behaarul Anwaar)

The Prophet of Allah (s.a.w.s.) has also mentioned the following tradition:
"One who does nor care from which way he earns wealth in this world will be sent to Hell in Qiyamat and I shall not care from which way he is made to enter it." 
(Behaarul Anwaar)

Allah does not provide unlawful livelihood

Maybe, those who do not refrain from unlawful earnings are afraid that if they give up this chance they may suffer poverty and deprivation. This is just a false notion. It is merely a satanic thought because it goes against the Divine promise of lawful sustenance repeatedly mentioned in the Quran. It is unreasonable, as it is contrary to the numerous traditions of Ahlul Bayt (a.s.). The Almighty Allah has promised to provide sustenance to each and every creature. The Divine promise is never unfulfilled. Allah only tests the believers to see if they strive patiently to acquire lawful livelihood or act impatiently and deviate. Whatever sustenance is decreed is surely received. It is only the impatience of the people and the weakness of their faith that makes them leave the path of lawful earnings and stray towards illegal occupations. When a person does this he fails the test. Allah deprives this person of the lawful sustenance that was in his destiny. Allah has not decreed for anyone unlawful sustenance.

No one dies without receiving his decreed sustenance

On the occasion of the last Hajj, the Holy Prophet (s.a.w.s.) addressed the Muslims in the precincts of the Masjidul Haraam: 
"Know that, the trustworthy Spirit (Jibraeel) has informed that no creature dies till he has received his destined sustenance.

Then fear Allah and do not vie among yourself in earning your livelihood. If there is some delay in receiving your sustenance, it must not be that you pursue it in disobedience to Allah. Verily, Allah has distributed only halaal sustenance to every creature. He has not destined haraam sustenance to anyone.

Hence one who fears Allah and acts with patience, Allah shall bestow upon him His sustenance through lawful means. But one who abandons purity and takes up haraam methods, a similar amount shall be decreased from his lawful sustenance. He shall be made to account for his haraam earnings on the Day of Qiyamat. Allah the Almighty has prohibited it in the following words: "...and do not substitute worthless (things) for (their) good (ones)..."
(Surah Nisa 4:2)

It should not be that in a hurry to obtain livelihood you obtain it through illegal ways, before Allah provides you with the halaal sustenance that He had decreed for you."
(Al Kafi)

Deprived of halaal food

One day, Amirul Momineen Ali (a.s.) reached the mosque and alighted from his mule. He entrusted his animal to a person and entered the mosque. The man pulled out the saddle and ran away leaving the mule unattended.

When Ali (a.s.) returned, he was holding two dirhams. He intended to give them to the man who had looked after the mule. He found the mule without the saddle. After reaching home he gave the same two dirhams to his slave for the purchase of another saddle. The slave went to the bazaar found the same rein. It came to be known that the thief had sold the stolen rein for two dirhams. It was the same amount that he could have earned in a lawful way. When the slave related the whole incident to Ali (a.s.), he said, 
"By abandoning patience man converts his halaal sustenance into haraam. Though he does not receive more than what is in his destiny." 
(Lailail-Akhbaar)