My dad told me that the Muslim caliph Abu Bakr instituted a minimum wage-esque policy during his rule. Was this the first time it happened? Were there other empires or people among whom this had ready happened?
I don't know about Muslim Caliphs but, as far as I'm aware, the first recorded minimum-wage laws were in New Zealand and in Australia.
In 1894, the New Zealand government passed the Industrial Conciliation and Arbitration Act. This gave legal recognition to unions, and allowed them to take pay claims to a Conciliation Board which could make binding decisions about the award conditions for an industry. There was also an Arbitration Court to appeal to if the Conciliation Board's decision was unacceptable to the employer or the union. Effectively, this Board and Court set minimum wages in various industries across New Zealand.
In 1896, the Victorian colonial government passed an amendment to their Factories and Shops Act which created a wages board. This wages board didn't set a universal minimum wage, but it did set minimum wages in the baking, boot-making, mens' clothing, and women's and girls' underclothing industries. This approach spread to other colonies (and, after Federation, to other states).
In 1904, the new federal Australian government passed laws to create a Commonwealth Court of Conciliation and Arbitration which, like its New Zealand predecessor, could rule on wages and awards and effectively set minimum wages. This Court of Conciliation and Arbitration made a landmark ruling in 1907 when it ruled that there was such a thing as a "living wage":
This influenced the future direction of minimum wages, by linking them to the cost of living, rather than being just an arbitrary amount.