Nejatullah:

“The rate of interest – free of intervention by policy makers – would, according to economic theory, be determined by the rate of return in the real economy.”

Muhammad Anas Zarqa:

“…the discount rate and the interest rate are two distinctly different things. Discounting prospective cash flows of projects promotes efficiency in investment and is quite acceptable Islamically. Discounting may be based entirely on rates of return in an Islamic economy which abolishes interest.”

Source: Riba, Bank Interest and the Rationale of its Prohibition – Mohammad Nejatullah Siddiqi