Is the agreement between spouses to pay a sum of money as charity upon verbal abuse towards others considered a bid'ah (innovation in religion)?

There is no innovation (bid'ah) in vowing to fast or give charity to rid oneself of backbiting; rather, it is a legitimate means of disciplining the soul. Some of the predecessors (Salaf) did this, such as Ibn Wahb, who vowed to fast and then give charity whenever he backbit. This indicates the fruit of beneficial knowledge. It must be noted that this does not negate the need for sincere repentance from backbiting.