Being Stern to Disbelievers

I have read in different places, that being stern to disbelievers is actually a good thing. However when I read hadith and stories of the Prophet (pbuh) I don't find anything of that nature. So I was wondering where this stern to disbeliever has a basis in Islam.

Walaikum assalam wa rahmatullah,

“Being stern” entails responding with strength, as befitting the situation according to the standards of the Sacred Law as soundly understood by Sunni scholarship (and not the calls of ultimately empty emotion), when unbelievers show enmity to Islam.

Otherwise, we have been commanded to deal with unbelievers with excellence, for good conduct is the best of calls to Islam.

Wassalam,

Faraz Rabbani
faraz@sunnipath.com
hanafi@sunnipath.com 

Imam Abu Hanifa (Allah have mercy on him) said, "Fiqh is to know one's self: what is for it and against it."