What is the ruling on inward anger towards parents, and is there any scholarly disagreement regarding this?

Anger itself is not something a person is held accountable for, as it is an uncontrollable emotion. Rather, one is held accountable for the bad words or actions that result from it, or for not avoiding its causes.

Al-Baji interpreted the hadith "Do not get angry" to mean not to proceed with what anger calls for. If anger leads to a bad consequence, such as harming one's parents, then that is considered an act of disobedience (to parents).

To manage anger, it is advised to remove oneself from the situation until one calms down, as Ali ibn Abi Talib, may Allah be pleased with him, did when he left his house for the mosque when he was angry with his wife Fatima, may Allah be pleased with her, fearing that he might utter something inappropriate.