Is it wrong to not pay half in this situation?

Ok so here's the situation: My drummer needed to get to another gig quickly so he got a cab so I jumped in. I could have gotten a lift with a mate as well...anyway when we got to the place we paid with the money made from the previous gig, and he wants me to pay half. I feel that I don't have to as he needed to get there regardless. I said I'm happy to chip in, but not pay half. What do you think?