Longstreet quote about reserves

[vtsaogames]

Please help me, hive mind.

I recall Longstreet making a statement to the effect that once a commander had committed his last reserve, he nothing left to do. He proved this wrong when his staff manned an abandoned gun at Antietam, unless you count his staff as his last reserve.

Anyway, anyone know that quote? And where it came from would be a bonus.

Thanks in advance.