Clarification of the Capital in a Salam Contract

The questioner:
And is it permissible for me to become a man, or to make a salam for a man, in a new matter?

The Shaykh:
Is it permissible for me?

The questioner:
And is it permissible for me to exchange a man’s matter, a new one, which he was returning to me on a deferred basis, in place of two sa’ (a dry measure of about 3 kg) in a matter where he turned it around?

The Shaykh:
No, this is riba (usury or interest). The meaning of salam is that you advance dirhams on the condition that he returns to you dates in the future, or wheat in the future. You advance dirhams; the capital of the salam must be in dirhams. It is not permissible for it to be in dates or in wheat. Yes.