Hakim bin Hizam (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings of Allah be upon him) forbade me from selling something which was not in my possession. Imam Tirmidhi says:
1- This hadith is Hasan (good).
2- Ishaq bin Mansur says: I asked Ahmad bin Hanbal: What is the meaning of the prohibition of combining sale with a loan? He said: Its form is that a man gives a loan to someone and then sells to him, taking a higher price for the goods. And it is also possible that someone gives an advance (salam) to someone for something and says: If you are unable to provide the money, then you must sell me this item. Ishaq (ibn Rahwayh) also said the same as Ahmad said.
3- Ishaq bin Mansur said: I asked Ahmad about the sale of something for which the seller is not liable. He replied: (This prohibition) in my view is only with the sale of food until it is possessed, that is, possession means liability. Ishaq bin Rahwayh also said the same as Ahmad said, but this prohibition applies to everything that is measured or weighed. Ahmad bin Hanbal says: When the seller says: I am selling you this cloth on the condition that its sewing and washing are my responsibility, then this form of sale is of the type of two conditions in one sale. And when the seller says: I am selling you this cloth on the condition that its sewing is my responsibility, or the seller says: I am selling you this cloth on the condition that its washing is my responsibility, then there is no objection in this sale, this is only one condition. Ishaq bin Rahwayh also said the same as Ahmad said.