Re: Requirements for fight
Jabla bin Ayham became murtid after the Battle of Yarmouk where he fought for the Byzantines. He converted to Islam after the battle and then became Christian again and returned to be sheltered by them.
Byzantium would not have rescinded their support because they viewed themselves as being the greatest power in the world. Events were cast in motion that would lead to their destruction - Muslims seized their territory because they forefeited it through supoprt for the Ghassanid murderers; Byzantium hated the Muslims for taking their land and fought to take it back at every opportunity. They because an existential threat to the Ummah and had to be destroyed, fulfilled by Mehmed the conqueror 800 years later.