All im gonna say is that im a little angry about you using that quote, its completely out of context. The quote was referencing the Battle of Badr. The "unbelievers" were the Pagans of Makkah were going to kill Muslims in Madinah. He wasn't telling Muslims to kill anyone who wasn't Muslim, he was just saying he was going to help defend the Muslims during the battle, the Pagans of Makkah had 1000 soldiers, meanwhile the Muslims had a mere 300 soldiers. Please don't take things out of context.