When I read about marriages in Islam, sometimes I see this:
... A husband, therefore, has the responsibility of taking care of his wife, protecting her, defending her honor, and fulfilling her needs regarding her religion and her worldly life. ...
He should defend her whenever she is slandered or spoken ill of behind her back.
However, I'm not sure how reliable these sources are. We also encounter the problem: How can I practically determine what "should" means?
Question: Is a Muslim husband required to defend the honor of his wife if someone speaks negatively of her?
I'm seeking some solid evidence (e.g. quotes from the Qur'an or Sunnah, or fatawa whose opinions are derived from reliable sources).
The current answer seems to have misunderstood the question. I'm not asking if a husband is forbidden from speaking negatively about his wife; I'm asking if it's sin for him to not defend his wife when someone else speaks negatively of her. Or, at least, if it's largely expected of a husband to defend his wife's honor in such circumstances.