What is the ruling on mixing cow's milk with powdered (dried) milk to increase production and trade it?

There is no objection to mixing cow's milk or other types with powdered milk, provided that this is clarified to the buyer. Concealing it is considered forbidden deception and fraud, as the Prophet, peace and blessings be upon him, said: "Whoever deceives us is not of us," and his saying: "The two parties to a transaction have the choice as long as they have not separated. If they are truthful and clarify, they will be blessed in their transaction. But if they lie and conceal, the blessing of their transaction will be effaced."