I heard the Messenger of Allah ﷺ say, "If you pursue people's faults, you will corrupt them, or nearly corrupt them."Abu Darda said, "A word that Muawiya heard from the Messenger of Allah ﷺ, by which Allah the Exalted benefited him."
سمعت رسول الله ﷺ يقول: إنك إن اتبعت عورات الناس أفسدتهم، أو كدت أن تفسدهم. فقال أبو الدرداء: كلمة سمعها معاوية من رسول الله ﷺ نفعه الله تعالى بها.
Abu Dawud (4888), Ibn Hibban (5760), and Bayhaqi in Kubra (8/333) all narrated it via Muhammad bin Yusuf Firyabi, from Sufyan (that is, Thawri), from Thawr, from Rashid bin Saad, from Muawiya, and he mentioned it. Its chain of transmission is sahih.His saying, "If you follow..." means that if spying is done for the purpose of uncovering people's private matters and faults, and exposing them publicly, then this is undoubtedly a great source of corruption. But if it is done to preserve security and safety and to identify saboteurs and troublemakers, then this is an obligation upon the state, in order to protect society and safeguard people's property, honor, and lives.As for what is reported from Abu Hurairah, who said that the Messenger of Allah ﷺ said, "One of you sees the speck in his brother's eye but forgets the log in his own eye," the correct view is that it is only attributed to Abu Hurairah and not raised to the Prophet.Ibn Hibban (5761) narrated it from Abu Aruba, who said, Kathir bin Ubayd told us, who said, Muhammad bin Himyar told us, from Jafar bin Barqan, from Yazid bin Asam, from Abu Hurairah, and he mentioned it as raised to the Prophet.Kathir bin Hisham Kullabi narrated it, as found in Zuhd by Imam Ahmad (p. 178), and Miskin bin Bukayr Hadhdha narrated it, as found in Adab al-Mufrad (592), both of them from Jafar bin Barqan, from Yazid bin Asam, with this same chain, but attributing it only to Abu Hurairah and not raising it to the Prophet.The version attributed only to Abu Hurairah is more sound than the one raised to the Prophet, because its narrators are more numerous and more reliable in memory, and Muhammad bin Himyar, though truthful, was alone in raising it to the Prophet and was not corroborated by anyone else. This proverb was well known before Islam, so perhaps Muhammad bin Himyar erred in attributing it to the Prophet ﷺ. I have read that the first person to use this proverb was Isa .