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.[Abu Dawud]. (RU)
App reference (RU): Book 18, Hadith 62 (RU)
Arabic/English book reference (RU): Book 18, Hadith 1572 (RU)