Is it permissible to pay a company part of an amount in cash now, provided that the remainder is received from the company after a month?

If you are asking about a man who has a deferred debt with a company, and he wants you to give him a smaller sum of money immediately, on the condition that you collect the full amount from the company a month later, then this transaction is usurious. This is because it is the sale of a deferred debt for immediate cash, which is a form of riba an-nasi'ah (usury of delay). It also involves riba al-fadl (usury of surplus) due to the exchange of currency of the same kind for a greater amount. Thus, both types of usury, al-fadl and an-nasi'ah, are combined in it. Ibn Rajab mentioned in "Al-Qawa'id" that selling sukuk (debts) before taking possession of them, if the debt is in cash and sold for cash, is impermissible without dispute, because it constitutes currency exchange with a delay (sarf bi nasi'ah).