Transfer file from ssh session to another ssh session

[Jan Hausler <jan.hausler@xxxxxxxxxxxx>]

Hello everyone,

I recently came across the following scenario:

I need to connect to server A and from within server A to server B to copy
a file from server B to server A. I can successfully connect to both of these
separately, but how to open a ssh/sftp session from within another one is
beyond me so far - any help is appreciated.

Thank you,
Jan Häusler