As for how the `Adliyya define `isma, their definition is the most appropriate. The gist of the correct part of their definition is that (`isma) is a divine disposition that prevents the act of disobeying and intending to do so while retaining the capability to do it.
The ma`sum abstains from all the things that God has prohibited.
Shaykh Ahmad al-Ahsa’i, Kitab al-`isma (Book of Infallibility), introduction. In the Baha’i writings, `isma is translated as “infallibility,” “sinlessness,” and “protection.” Ma`sum is a person characterized by `isma. The `Adliyya (“followers of justice”) are the Shia and the Mu`tazilites, who believe that God’s justice requires that humans act of their own volition and thus merit the resulting reward or punishment.
In Shaykh Ahmad’s book, the synonyms of disobeying (ma`siyya) are sin (dhanb), negligence (ghafla), venial sin (saghira), mortal sin (kabira), shortcoming (taqsir), and evil deed (sayyi’a). His synonyms for negligence (ghafla) are forgetfulness (nisyan), inattention (sahw), and error (khata’). All these words have to do with the morality of an action.
The final word, khata’, is found in `Abdu’l-Baha’s Will and Testament in reference to the Universal House of Justice as “the source of all good and freed from all error (khata’).”