hadith tell of rules of naskh being passed down directly from Muhammad's closest Companions (sahabah) and future Muslim leaders — others believe it more likely ideas about naskh originated later. Ahman Hasan speculates that the idea of the abrogation of certain Qur'anic verses "emerged" early in the history of Islam when commentators and the jurisconsults seeking to reconcile the "apparently contradictory verses", looked to the Quranic verses such as Q.16:110 — "... We put a revelation in place of (another) revelation ..." — to develop a theory that some later verses replaced the commands of earlier ones. John Burton argues that naskh was first employed by Islamic scholars ("usulis") in the second century of Islam working to develop principles (usul al-fiqh) for the Islamic law (fiqh) and seeking to explain why some fiqh rulings were not founded on Quranic/Sunnah revelation. By this time the Islamic empire spanned three continents and fiqh had been established in the different regions but usulis found rulings in certain verses of the Quran and parts of the Sunnah had been ignored in their formulation. To explain this, Burton argues, they developed the concept of naskh to declare that the verses/parts had been abrogated. In theory, naskh formed part of a hierarchy of techniques used by scholars of Islamic law working with hadith. Scholars first strove to "harmonize" hadith, (i.e. to make them fit together by reinterpreting them). If that failed they would look for signs of abrogation (that one saying/doing/inaction by Muhammad was earlier than the other and had been replaced by the later saying/doing/inaction). If there was no opportunity for abrogation, they would check the isnad—chains of transmission of the hadith—to see if the transmission of one hadith was superior to another. Finally, if they found no difference in the isnad, they would approve the hadith they found "closest to the overall message of the Quran and Sunnah". Problem But according to scholars such as David S. Powers and John Burton, while the doctrine of abrogation may have cleared up contradictions, it "poses a difficult theological problem" because it seems to suggest God was changing His mind, or has realized something He was unaware of when revealing the original verse. For an eternally all-knowing deity this was theologically impossible and logically absurd — in fact an act of "unbelief" in Islam itself. Also foreclosing on the possibility of any improvisation of Quranic verses was