Allah SubhanaHu Wa Taala Says, What Is Rah-Bul-a-L-Am-Een?

Musa'alais Hsallam went to Firahun and told him, it is Ilma'ana, Bani Isra'im. He said we want you to release them and stop oppression,. You are not the God and so on. Firahun laughed at them, him and his people. Allah subhanaHu Wa Taala says he didn't even say who rah-bul-a-l-am-een was. The Prophet Musa Allahi Salaam responded by saying whoever created the skies and the earth deserves to be worshipped alone.