Mixing people’s gold when working it
Question

                What is the ruling on one who hands over his gold to a goldsmith to work it, and his gold may be mixed with the gold of others when the gold is melted, but when he takes it back from the goldsmith he gets the same weight of gold as that which he handed over?.
Praise be to Allah.The goldsmith should not 
    mix people’s gold together; he should keep it all separate if the standard 
    of the gold varies.

     But if there is no difference in the standard of the gold, 
    then there is nothing wrong with putting them together because it does not 
    do any harm.