A man once asked Imam Ahmad, ‘I sometimes find myself in a gathering where the Sunnah is mentioned, but no-one apart from me has more knowledge of it. Shall I speak up and say something?’

Imam Ahmad then said, ‘State what the Sunnah is, but do not argue over it.’

The man then repeated his statement and so Imam Ahmad said, ‘I only see you to be an argumentative man!’

And this is what Malik (rahimahullah) meant in his saying (after informing people of the Sunnah), ‘And if they don’t accept it from you, then be silent.’

Mu’tamir ibn Sulayman: ‘I heard my father say, ‘You can never get a man to listen to you when you have just angered him.’

- Al-Adab al-Shar'iyyah, by Ibn Muflih al-Maqdisi [pg. 307]

Point of benefit: Advise people of correct actions, the Sunnah, and the proper manner of conduct etc, but don’t push them to the point of anger and arguments because getting advice through to a person in that state is like trying to force back water flowing from a tap… Instead, let the heat die down, let the issue close for a while and then try again when things are calm.

http://fajr.wordpress.com/2011/04/12/speak-up-but-dont-argue/