1. Don't spread rumours. Whenever you hear something which concerns your collective life, communicate it to the appropriate authorities so as to make them reach a correct conclusion after proper investigation:
(4:83) "When there comes to them some matter touching (public) safety or fear, they divulge it, although their attachment and obedience to the (Divine) System requires that they had only referred it to the Rasool (central authority) or those charged with authority amongst them (officers of the lower ranks); in case they refer it to them, the specialists could verify and ascertain the truth."
At yet another place it is said:
(49:6) "O you who believe! If a mischief-maker comes to you with any news, ascertain the truth, lest you should harm people unknowingly, and afterwards have to feel ashamed for what you have done."
2. When you hear a rumour against somebody, your first reaction ought to be that it is a calumny. In Surah "An-Noor" (24th Chapter of the Quran) an event has been mentioned concerning a noble, chaste lady, about whom somebody started a rumour which got spread in the society.
(24:12) "When you heard it, why did you not react with a favourable view and declare it as a clear calumny Why did not believers __ men and women __ when they heard of the affair, thought good of your own fold and said: It is a manifest calumny."
It was further said:
(24:15-16) "When you received it on your tongues and spoke with your mouths that of which you had no knowledge, and you deemed it a trifle, while with Allah it was serious. And why did you not, when you heard it, say: It beseems us not to talk of it. Glory be to Thee! This is a great calumny"