O YOU who have attained to faith! No men shall deride [other] men: it may well be that those [whom they deride] are better than themselves; and no women [shall deride other] women: it may well be that those [whom they deride] are better than themselves. And neither shall you defame one another, nor insult one another by [opprobrious] epithets: evil is all imputation of iniquity after [one has attained to] faith; and they who [become guilty thereof and] do not repent - it is they, they who are evildoers!
Al-Hujurat (The Dwellings) Verse 12
Allah's Apostle said, "Whenever you hear the Adhan, say what the Mu'adhdhin is saying.
Sahih Bukhari: Volume 1, Book 11, Number 585