Running status can be used with any message that has a status byte that contains a channel (status bytes 80 to EF). If you want to send two or more sequential messages that would have the same status byte, you can omit the status byte from the second and later messages.
You can download the main MIDI specification as a PDF file from the following page on this site: Specs -> The MIDI 1.0 Specification ->
The Complete MIDI 1.0 Detailed Specification. (You have to log in with your account to download the PDF file.) Running Status is described on PDF pages 91 to 93.