[21].Al-Anbiya [The Prophets]: Ayat 87-88

Ayat 87. And (remember) Dhan-Nun (Jonah), when he went off in anger, and imagined that Allah shall not punish him (i.e. the calamites which had befallen him)! But he cried through the darkness (saying): Lâ ilâha illa Anta [none has the right to be worshipped but You (O Allah)], Glorified (and Exalted) are You [above all that (evil) they associate with You]. Truly, I have been of the wrong-doers."

Ayat 88. So Allah answered his call, and delivered him from the distress. And thus We do deliver the believers (who believe in the Oneness of Allah, abstain from evil and work righteousness).

[Tafseer] Dhu al Nun, "the man of the Fish or the Whale", is the title of Jonah (Yunus), because he was swallowed by a large Fish or Whale. He was the prophet raised to warn the Assyrian capital Nineveh. When his first warning was unheeded by the people, he denounced Allah's wrath on them. But they repented and Allah  forgave them for the time being. Jonah, meanwhile, departed in wrath, discouraged at the apparent failure of his mission. He should have remained in the most discouraging circumstances, and relied on the power of Allah; for Allah had power both over Nineveh and over the Messenger He had sent to Nineveh . He went away to the sea and took a ship, but apparently the sailors threw him out as a man of bad omen in a storm. He was swallowed by a big Fish (or Whale), but in the depth of the darkness, he cried to Allah and confessed his weakness. The "darkness" may be interpreted both physically and spiritually; physically, as the darkness of the night and the storm and the Fish's body; spiritually as the darkness in his soul, his extreme distress in the situation which he had brought on himself. Allah Most Gracious forgave him. He was cast out ashore; he was given the shelter of a plant in his state of physical and mental lassitude. He was refreshed and strengthened, and the work of his mission prospered. Thus he overcame all his disappointment by repentance and Faith, and Allah accepted him. 

Hazrat Abu Saeed & Abu Hurairah (May Allah be pleased with them) reported: The Messenger of Allah [SAWW](PBUH) said, "Never a believer is stricken with a discomfort, an illness, an anxiety, a grief or mental worry or even the pricking of a thorn but Allah will expiate his sins on account of his patience".

[Al-Bukhari Book 07, Chapter 70, Hadith # 545] 

Lesson : as mentioned above in Surah Al-Anbiya Ayat 87."Allah shall not punish him (i.e. the calamites which had befallen him)!" This Hadith mentions the special Grace and Mercy of Allah for the Muslims. It relates how Allah turns the hardships and troubles suffered by a Muslim into a means of expiation for his sins. But this is only possible if the believer exercises patience. However, if he starts wailing instead of showing patience then beside suffering hardships, he would be deprived of the reward which lies in bearing them patiently. Thus, he shall have to take the burden of additional sins also.