Leaving each other before delivering the exchanged amount in full

Q: A man, who wants to exchange 500 riyals, went to a grocer who had only 300 riyals which he gave to the man to give him the remainder later on. Another person objected to it judging it to be a usurious transaction. Please, inform us about it, May Allah guide you and show you the right way! As-salamu `alaykum warahmatullah wabarakatuh (May Allah's Peace, Mercy, and Blessings be upon you!)

A: Those who exchange money may not separate before each of them receives the whole exchanged amount. Accordingly, it is impermissible for the man who gave 500 riyals to another to exchange to take 300 riyals in advance and take the remainder, even soon, after separation. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.