Musannaf Ibn Abi Shaybah

Badeel Al-Uqeeli came to Hazrat Ibn Sireen and there was a man with him, and he said, "This person is asking about the transaction of sarf (exchange of currency)?" He replied: The Prophet (peace be upon him), Hazrat Abu Bakr, Hazrat Umar, and Hazrat Uthman (may Allah be pleased with them) forbade it.

Hazrat Saeed bin Al-Musayyib narrates that Hazrat Ali (may Allah be pleased with him) and Hazrat Uthman (may Allah be pleased with him) forbade the transaction of sarf (exchange of currency).

Hazrat Abu Umamah says that exchange is also usury.

Hazrat Ali (may Allah be pleased with him) was asked about sarf (exchange of money). He said: This is riba al-qardh (usury of loan).

Hazrat Abu Al-Aliyah says that if I pass by the house of a person who deals in currency exchange and I feel thirsty, even then I will not ask him for water.