What is the ruling on tearing the lip and eating what was torn?

Intentionally tearing one's lip and eating it is not permissible if it causes harm or pain to oneself, based on the Prophet's (peace be upon him) saying: "There should be neither harm nor reciprocating harm." And based on Ibn Hazm's statement: "They [scholars] have agreed that it is not permissible for anyone to kill himself, nor to sever any of his limbs, nor to inflict pain upon himself except for medical treatment involving the removal of a diseased limb." However, if this occurred by mistake or forgetfulness, then there is no blame, based on the Prophet's (peace be upon him) saying: "Indeed, Allah has overlooked for my nation mistakes, forgetfulness, and what they are coerced into."