Here's the original song:
The song was written by Maurice White (who sadly passed away on February 2nd 2016), Al McKay and Allee Williams a struggling songwriter in L.A., who got offered the chance of a lifetime by Maurice: to co-write Earth, Wind & Fire's next album.
Willis recalls: As I opened the studio door, they had just written the intro to "September". Because the lyrics weren't finished yet Maurice was using a go-to phrase singing: "Ba-dee-ya, do you remember, Ba-dee-ya, dancing in September. "
Willis said: "We are going to change "bee.da-ya" to real words, right?" But at the final vocal session Maurice was still singing "bee-da-ya" and so Willis asked him: "What the f---- does "ba-dee-ya" mean?" and White answered: "Who the f--- cares?" Later on Willis resumed, that this was one of her greatest lessons in songwriting ever, which was never let the lyric get in the way of the groove.