Which preposition to use with bak

to Occurrences 1%

so I said that I was under an oath to a god to drink nothing beautiful; and they asked me if he could not be appeased by a prayer, and I said, "In nowise," and went towards the dance; and they commiserated me and abused that god bitterly, thinking to please me thereby, and then they fell to drinking bak to the glory of Singanee.

Which preposition to use with  bak