Salaams

From what I understand the Prophet pbuh used to pray before the Night of Isra (his Ascension to the Heavens) where Allah swt legislated the five daily prayers.

We're also told that the prophets before Muhammad pbuhused to pray to God - i.e. perform salat. If Salat was already ordained - what was the difference between their salat and the one that was legislated to prophet Muhammad pbuh?