First redacted on early March 2018.
After some time with Prosody 0.10 on Debian 9, I wanted to test Ejabberd. You'll find below steps for doing such migration.
The most recent version can be found in Stretch's backports repository:
cat <<EOF | sudo tee /etc/apt/sources.list.d/backports.list deb http://ftp.debian.org/debian stretch-backports main