Is it permissible to declare as an innovator (mubtadi') one who adopts and acts upon a weak hadith?

Acting upon a weak Hadith concerning the virtues of deeds that fall under a general principle is permissible according to most imams, provided that its falsity is not known, and it is not used as proof for prohibition or obligation. Shaykh al-Islam clarified that Ahmad ibn Hanbal and the scholars before him used to categorize Hadith into authentic and weak. The weak, in their view, was divided into weak-abandoned and weak-good, the latter being admissible as proof. One must be cautious about declaring a specific person an innovator except after the fulfillment of conditions and the absence of impediments, for the Salaf used to dispute matters without accusing anyone of disbelief or فسق (transgression).