Vin Scully gave an interview to Daniel Riley of GQ in which he comments and reflects upon his greatest calls. There are audio recordings of the interview excerpts if you click the link; here’s GQ’s roughly transcribed version of how Scully’s comments on Kirk Gibson end:

… So when he hits the home run, the whole building… from the empty dugout to the walk, to him suddenly using the bat as a cane… it was just the most theatrical home run. And the place went crazy. I don’t know where it came from, but out came a line that later on I thought only could’ve come from The Boss. That line, ‘In a year of the improbable, the impossible has happened’ — which, I must admit, is a pretty good line — it just totally came out of nowhere. My heart, that’s where it came from, and God helped me out.”