and blasphemy. Historian David Cook writes that "it is only with the 'Abbasi caliphs al-Mu'taṣim (218-28 AH/833-42 CE) and al-Mutawakkil (233-47 /847-61) that we find detailed accounts" of apostates and what was done with them. Prior to that, in the Umayyad and early Abbasid periods, measures to defend Islam from apostasy "appear to have mostly remained limited to intellectual debates" He also states that "the most common category of apostates" — at least of apostates who converted to another religion — "from the very first days of Islam" were "Christians and Jews who converted to Islam and after some time" reconverted back to their former faith. Some sources emphasize that executions of apostates have been "rare in Islamic history". According to historian Bernard Lewis, in "religious polemic" in the "early times" of Islam, "charges of apostasy were not unusual", but the accused were seldom prosecuted, and "some even held high offices in the Muslim state". Later, "as the rules and penalties of the Muslim law were systematized and more regularly enforced, charges of apostasy became rarer." When action was taken against an alleged apostate, it was much more likely to be "quarantine" than execution, unless the innovation was "extreme, persistent and aggressive". Another source, legal historian Sadakat Kadri, argues execution was rare because "it was widely believed" that any accused apostate "who repented by articulating the shahada [...] had to be forgiven" and their punishment delayed until after Judgement Day. This principle was upheld "even in extreme situations", such as when an offender adopted Islam "only for fear of death" and their sincerity seemed highly implausible. It was based on the hadith that Muhammad had upbraided a follower for killing a raider who had uttered the shahada. The New Encyclopedia of Islam also states that after the early period, with some notable exceptions, the practice in Islam regarding atheism or various forms of heresy, grew more tolerant as long as it was a private matter. However heresy and atheism expressed in public may well be considered a scandal and a menace to a society; in some societies they are punishable, at least to the extent the perpetrator is silenced. In particular, blasphemy against God and insulting Muhammad are major crimes. In contrast, historian David Cook maintains the issue of apostasy and punishment for it was not uncommon in Islamic history. However, he also states that prior to 11th century execution