Sharia law bans lending money at interest, denouncing it, as Christianity used to, as ‘usury.’ So how come there can be such a thing as ‘Islamic banking?’

Sharia commercial law emerged as a way of regulating trade in pre-capitalist times in those parts of the world where Islam was the dominant religion. This trade was fairly extensive (think Silk Road) and involved buying goods in one place and transporting them to another where they could be sold at a higher price that would more than cover the expenses. Buying cheap to sell dear. Mohammed himself had been such a merchant.