If you have not read the latest article by Mathieu Tillier and you’d be happy to practice your French, I highly recommend you
Mathieu Tillier has gathered a corpus of epigraphic invocations (duʿāʾ) which he compares with invocation formulae contained in ḥadīth narratives. He covers the first three centuries of Islamic history and anaylses in details what he has coined the “prophetisation” of ḥadīth narratives, whereby formulae attributed to anonymous figure slowly become the saying of companions, successors and finally Muḥammad. His comparative approach, in which he combines lexical and textual analysis, allows him to uncover the rare formulae that could be traced back to the first century of the Islamic era and were preserved untouched in the literature. His scrupulous comparison also highlights the evolution of the different phenomena observed regarding the formulae that remained untouched, those which were attributed to non-prophetic figures and finally the ones which were ‘prophetised’, i.e. attributed to the Prophet Muḥammad. It is to be hoped that this well-documented work will inspire more similar interdisciplinary studies and help us understand better the ḥadīth literature in its historical context.