How to automate connecting to multiple network devices, running a command and saving the output to a file?

I have to run a command on around 1000 network devices and save the output to a file. In a file I have a list of all the network device names that have to be connected to using SSH. I then have to run a command, let's say show interface description for instance, then save the output to a file. The devices are all set up with a generic username and password that is the same on all devices. So basically I need a script to run these commands on all devices in the list file:

ssh user@device1
password: passwordhere
user@device1> show interface description
user@device1> exit

Then save all the output to a file. I am using Red Hat Enterprise Server.