How to do Sales order no tracking in Purchase Order

Hi All,

I have a sales order say FG001 - 500Nos

for that I have to make a Purchase order   say, RM01-150Kgs

Now I want to know against which sales order I have done this. Means I want   Sales order no to be tracked in purchase order. Then I have some cross  analysis. I tried procurement wizard, but that will work if my  sales is the purchase item too(TRADING). MRP wizard also not meet my requirement, Can anyone give some suggestion.

Thanks,

Pravin.