What were y'all doing in a hotel?
That might be more cause for sinning that taking a bible that was placed there.
I'd put the hotel room bible in the same category as the hotel toiletries, they are there for your use, and if you want to take them, g'head. Most bibles I've seen, generally request a donation for the bible, but it's only suggested. Taking the towels or the bathrobe (or blowdryer, sheets, etc) is stealing...