Hadith: No fatigue, disease, sorrow, sadness, harm, or distress befalls a Muslim, even if it were a prick of a thorn, but Allah will expiate some of his sins thereby

عن أبي سعيد وأبي هريرة رضي الله عنهما مرفوعاً: «ما يُصيب المسلم من نَصب، ولا وصَب، ولا هَمِّ، ولا حَزن، ولا أَذى، ولا غَمِّ، حتى الشوكة يُشاكها إلا كفر الله بها من خطاياه».
[صحيح] - [متفق عليه]

Abu Sa‘īd and Abu Hurayrah may Allah be pleased with both of them) reported that the Prophet (may Allah's peace and blessings be upon him) said: "No fatigue, disease, sorrow, sadness, harm, or distress befalls a Muslim, even if it were a prick of a thorn, but Allah will expiate some of his sins thereby."
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

Hadīth explanation: Illness, grief, distress, sadness, calamities, fear, panic, etc. and any other adversities that afflict a Muslim, but expiate his sins and remove his shortcomings. If, in addition, someone adheres to patience and expects the reward from Allah, he will receive a reward along with the expiation of his sins. A person reacts to calamities in two ways: Sometimes, when he is afflicted, he remembers the reward for enduring an affliction with content, and he expects the reward from Allah. So, he will have two benefits for him: expiation of his sins, and increase in reward from Allah sometimes, he is heedless of the intention to expect the reward from Allah, so he feels grieved and distressed, which also leads to the expiation of his sins. Hence, he wins in all cases; either he wins through expiation of his sins and erasing of his mistakes, without receiving reward because he did not make his intention to be patient and expect the reward from Allah, or he wins both: expiation of sins and reward from Allah as mentioned. Therefore, when someone is afflicted with a hardship, even if it were the prick of a thorn, should remind himself of receiving reward from Allah; so as to receive reward along with expiation of his sins. This is a manifestation of Allah's grace and generosity; He puts a believer into a trial then rewards him for it or expiates his sins. Note: Erasing mistakes refers to the minor sins, not the major sins which are only erased through sincere repentance.