وَإِذَا قَرَأْتَ الْقُرْآنَ جَعَلْنَا بَيْنَكَ وَبَيْنَ الَّذِينَ لَا يُؤْمِنُونَ بِالْآخِرَةِ حِجَابًا مَّسْتُورًا 
Volume X of al-Tabari's massive chronicle is devoted to two main subjects. The first is the selection of Abu Bakr as the first caliph