My history professor said that there is no 'official' ending for medieval times.
He stated that there are various occurrences which could indicate the end.
I didn't find any information on the internet.
Are you sure he didn't mean the Hegira, Muhammed's emigration from Mecca to (later) Medina? It marks a significant point in Mohammed's life, and the birth of Islam (which is one of the transitional elements from late antiquity to early medieval).