Article: The Umayyads have met with a largely negative reception from later Islamic historians, who have accused them of promoting a kingship (mulk, a term with connotations of tyranny) instead of a true caliphate (khilafa). In this respect it is notable that the Umayyad caliphs referred to themselves not as khalifat rasul Allah ("successor of the messenger of God", the title preferred by the tradition), but rather as khalifat Allah ("deputy of God"). The distinction seems to indicate that the Umayyads "regarded themselves as God's representatives at the head of the community and saw no need to share their religious power with, or delegate it to, the emergent class of religious scholars." In fact, it was precisely this class of scholars, based largely in Iraq, that was responsible for collecting and recording the traditions that form the primary source material for the history of the Umayyad period. In reconstructing this history, therefore, it is necessary to rely mainly on sources, such as the histories of Tabari and Baladhuri, that were written in the Abbasid court at Baghdad.

Now answer this question: What was the tradition Arabic title used by caliphs?
khalifat rasul Allah