Salm bin Abi al-Ja'd سالم بن أبي الجعد · The Chapters on Business Transactions

"Do not meet the traders on the way, and whoever meets any of them and buys from him, the vendor has the choice of annulling the transaction when he comes to the marketplace.''

"The Messenger of Allah (ﷺ) forbade Gharar transactions. "

"I came saying. 'Who will exchange Dirham?' Talhah bin 'Ubaidullah, who was with 'Umar bin Khattab, said: 'Show us your gold, then come to us; when our treasure comes, we will give you your silver.' 'Umar said: 'No, by Allah, you will give him silver (now), or give him back his gold, for the Messenger of Allah (ﷺ) said: "Silver for gold is usury, unless it is exchanged on the spot."'