Hadithcore
Riyad as-Salihin, 1572

It has been reported that a man was brought before Abdullah bin Mas'ud (May Allah be pleased with him) because his beard was giving out smell of wine. Ibn Mas'ud said:

"We have been prohibited from spying (on Muslims) and finding faults (with them). But we can take to task only and only if the sin is overt. <b>[Abu Dawud]</b>.

وعن ابن مسعود رضي الله عنه أنه أتي برجل فقيل له، هذا فلان تقطر لحيته خمرًا، فقال‏:‏ إنَّا قد نهينا عن التجسس، ولكن إن يظهر لنا شئ، نأخذ به‏"‏‏.‏ حديث حسن صحيح رواه أبو داود بإسناد على شرط البخاري ومسلم‏.‏

References1 variant
In-Book Reference
Book 17, Hadith 62
Sharh · explanationclick to expand
<b>Guidance from the Hadith:</b><br> 1) If someone makes a claim against another, basing it upon spying, his claim is rejected.<br> 2) The Hadith encourages concealing the sinner who does not commit sin in public to give him a chance to repent of it.