Were the Sabeans Muslims?

I read this on the internet about the Sabeans: In brief, they did not reject the Prophets or regard it as obligatory to follow them. In their view, whoever followed (the Prophets) is blessed and saved, and whoever follows a path similar to that of the Prophets by virtue of his own reasoning is also blessed and saved, even if he did not follow the Prophets in specific terms. In their view, the call of the Prophets was true but there was no one specific route to salvation. Isn’t it all kufr? Also was a specific prophet sent to them?