The dating of Islamic traditions has so far remained dependent on internal analyses of the hadith corpus. However, a comparison between this corpus and documentary sources appears possible. Invocations engraved on rocks during the first three centuries of Islam can be compared with those attributed to the earliest authorities of Islam. The new method I propose, based on an analysis of lexical convergences between inscriptions and hadith, allows to approach the time when traditions were first put into circulation and to study the process whereby invocatory formulas were incorporated into the sunna and attributed to various authorities. In this way, it becomes possible to identify a historically plausible lexical nucleus in prophetic hadith and to understand how, by means of transmitters that I call “hubs,” ancient non-prophetic traditions became prophetic.