Is what Company (S2) did—purchasing materials for Company (S1) at its request, and transferring the full amount to a supplier who turned out to have a relationship with (S1) and would return part of the money to it, with Company (S2) taking a 10% profit margin—considered usury or a Sharia violation?

It is permissible for Company (A) to enter into a Murabaha contract for a purchase order with Company (B) at a specified profit margin, provided that Company (B) purchases the goods and takes possession of them before selling them to Company (A).

However, it is not permissible for Company (A) to collude with the supplier not to supply a portion of the purchased quantity in exchange for money, as this leads to usury (riba). Company (B) must take possession of the goods from the supplier before selling them. Company (B) may request the supplier to transport the goods to Company (A)'s premises and then sell them after confirming their arrival.