عن ابن عمر - رضي الله عنهما - ، أن النبي صلى الله عليه وآله وسلم نهى عن بيع الكالئ بالكالئ
The Prophet prohibited the selling of debts for debts
Note: One of the persons mentioned in the sanad of this Hadith is (موسى بن عقبة) and that is a mistake, for the narrator actually is (موسى بن عبيدة).
As for the authenticity of the Hadith, it is Da'eef.
Sources: Irwa' Al Ghaleel إرواء الغليل Chapter 5 Hadith 1382