I was reading a (poorly written) essay recently, wherein a hadith was mentioned but not fully quoted.  Allegedly, the classical *fuqaha* used it to forbid *bay' al-kali bil-kali* (Selling of debts for debts).

Beyond that, all I know is that it was reported by Ibn 'Umar, as related by al-Tabrani (*sic*).

What is this hadith?