Abu Jawza reported,

I heard Ibn Abbas issuing legal verdicts permitting currency exchange at unequal rates. So I gave verdicts based on that for some time. Then I met him later, and he had retracted that opinion.I asked him, "Why?"He replied, "It was merely an opinion I had formed. Abu Saeed Khudri narrated to me that the Messenger of Allah ﷺ forbade it."

Azami 5723

Sahih

عن أبي الجوزاء قال

سمعت ابن عباس يفتي بالصرف. قال: فأفتيت به زمانا قال: ثم لقيته، فرجع عنه. قال: فقلت له: ولم؟ فقال: إنما هو رأي رأيته. حدثني أبو سعيد الخدري أن رسول الله ﷺ نهي عنه.

الأعظمي 5723صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Sales
Chapter
Prohibited sales
Section
Those who say riba is only in credit transactions
Numbering
Jami al-Kamil 5723 (2nd edition)
Azami 5723