Do not be hasty in praising people or blaming them, for perhaps what pleases you from a person today will displease you tomorrow, and perhaps what displeases you today, will please you tomorrow. Indeed, people change. It is Allāh who forgives the sins. And Allāh is more merciful to his servant the day he meets him than a mother who lays out a bed for her child in an empty patch of land and feels [the ground]: if there is a risk of being stung, it will be her instead of him (her child), and if there is a risk of being pricked by a thorn, it will be her instead of him.
Al-Bayhaqī, Shuʿab Al-Īmān article 6177, and others.
The people will not cease to be well as long as they take knowledge from their seniors. When they take it from their juniors and their bad people, they will be destroyed.
Ibn ʿAbd Al-Barr, Jāmiʿ Bayān Al-ʿIlm article 1057.
A young man who had stolen was brought to ʿUmar (for punishment). He said, “By Allāh I have never stolen before this time.” So ʿUmar responded, “You lie, Allāh would not (or does not) surrender a servant of His on the first sin.”
Abū Dāwūd, Al-Zuhd article 56, and others. Graded ṣaḥīh by Ibn Kathīr and others.
No one who has learned Qurān and then forgotten it except due to a sin he has committed, because Allāh the most high said: وَمَآ أَصَـٰبَكُم مِّن مُّصِيبَةٍ فَبِمَا كَسَبَتْ أَيْدِيكُمْ Qurān 42:30 “And no calamity befalls you except due to what your own hands have earnt.” And forgetting the Qurān is one of the greatest calamities.
Qurān 42:30
When a sin is hidden it harms only the perpetrator, but if it is made apparent and not rectified, it harms all the people.
Ibn Waḍḍāḥ, Al-Bidʿah #287.
It is better for a man to leave one ḥarām dirham than to give one hundred thousand in charity.
Abū Bakr Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-ʿIlm 5:125.
“Beware of the sinful scholar (al-ʿālim al-fāsiq).” This reached ʿUmar, so he wrote to him in fear, “Who is the sinful scholar?” He wrote back, “I did not intend but good; this is when there is an imām (leader, taken as an example) who speaks knowledge, but practices sins, confusing the people, and thus they go astray.”
Al-Dhahabī, Siyar ʾAʿlām Al-Nubalāʾ 4:49.
It is reported that a man came to ʿAlī – Allāh be pleased with him – and asked, What do you think about a man who committed a sin? He replied, He must seek Allāh’s forgiveness and repent to Him. [The man] said, He did that, but then sinned again? [ʿAlī] said, He must seek Allāh’s forgiveness and repent to Him. The man again said, He did that, but returned to sin. [ʿAlī] said, He must seek Allāh’s forgiveness and repent to Him. The man said for the fourth time, He did, but then sinned again. ʿAlī then said, Until when? Then he said, He must seek Allāh’s forgiveness and repent to Him; and not give up until it is Shayṭān who is defeated [overcome].
Hunād b. Al-Sarī, Kitāb Al-Zuhd article 910
“How many kabā`ir (major, deadly sins) are there? Seven?” He replied, “They are closer to seven hundred than seven; except a major sin does not remain so if one (truly) seeks forgiveness [from Allāh], and a lesser sin does not remain so if one insists on continuously doing it (i.e. it becomes a major sin).”
Al-Tabarī, Al-Tafsīr article 9207, et al.
It is reported that Al-Fudayl b. ‘Ayyād – Allāh have mercy on him – said: Whoever sees a wrongdoing from his brother and then laughs in front of him has betrayed him. Abū Bakr Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-‘Ilm 5:115
Abū Bakr Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-‘Ilm 5:115