Cron job to back up DB to different FTP user?


Hi folks,
I have been running my WP site on DreamHost for several years but am new to Cron Jobs.
At present a colleague is helping me out by running a mirror of my main site. I created a new FTP user for him and cloned the main site onto a subdomain and he uses the data from that to apply on his server.
Every month I make a new backup of my main site’s database and put a copy in the /home folder of his FTP user, which results in the mirror site being updated.
I would like to know if it is possible for me to create a new cron job that would back up the DB, say on the 25th day of each month, into the folder where I currently put it manually?
If so, can you give me the code to use or point me to some documentation I could use?
I will be grateful for any help!