Slavic Pagan Religion

What we know about Slavic paganism? There are just few written sources that informs us about the Slavic Pagan Faith before Christianization. The first one is from the 6the century AD written by Byzantine scholar Procopius of Caesarea.
At the end of the 19th century in the southeast of Ukraine there was founded the Zbruch Idol. It is now in Kraków museum. But till today scientists provide discussion about its authenticity.