What ancient tradition of prayer is Jesus critical of in Matthew 6:7?
In praying, do not babble like the pagans, who think that they will be heard because of their many words. (NABRE)
But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking. (KJV)
And when you pray, do not keep on babbling like pagans, for they think they will be heard because of their many words. (NIV)
And in praying do not heap up empty phrases as the Gentiles do; for they think that they will be heard for their many words. (RSV)
And when you are praying, speak not much, as the heathens. For they think that in their much speaking they may be heard. (DRA)
I'm not asking for a personal interpretation of this passage, and I especially don't want opinions on the controversial matter of 'literal' prayers (which may or may not include the Lord's Prayer and the Psalms).
What is clear is that Jesus is making a reference to pagans/heathens (εθνικοι), who do something displeasing during their prayers (βαττολογησητε). The prayers of these pagans were presumably recognizable enough to be known both to the direct audience of Jesus and to the direct audience of Matthew. What do we know about these pagans and their way of praying? Was there a specific group? Are there any sources that describe the prayers of pagans at that time?
(An ideal answer might have the form "Jesus is talking about [pagan group], who would [way of talking] while praying ... that they did this is mentioned even in [extra-biblical source], which describes them as [quotation]".)