One of the more neglected testimonies about the beliefs and worship of the Slavs is the passage in William of Malmesbury's Gesta Regum Anglorum. Previous literature on the subject (L. Słupecki, R. Zaroff, M. Łuczyński) has neglected the aspects of source-criticism, focusing instead on the interpretation of the text before them. The availability of a new edition and digitized manuscripts has made it possible to revisit this issue. This analysis for the first time places William’s story not only in the context of his other works (Polyhistor, Vita Wulfstani), but also in the context of the sources he used. Special attention will be paid to William's information about Emperor Henry III and his wife Gunhild, thanks to which it will be noted that the chronicler mixed up different narrative threads. The speaker will also take up the question of possible dependencies between the Gesta Regum Anglorum and the Gesta Danorum of Saxo Grammaticus.