Sam & Dave - Hold On, I'm Comin'

allmusic:

Inspiration for a song can strike anywhere, including while you're in the john. At least that's what happened in the case of "Hold on I'm Comin'." While songwriter/producer David Porter was answering the call of nature, his partner Isaac Hayes yelled at him to come out so they could get back to work. Porter responded, "Hold on man, I'm coming." Feeling the beginnings of a hit song, Porter hastily exited, telling Hayes that that's a great title for a song.

Sam & Dave
Isaac Hayes