Sahih Bukhari Volume 3, Book 49, Hadith Number 869.

Narated By Abdullah bin Kab bin Malik : From Kab bin Malik, Abdullah bin Abu Hadrad Al-Aslami owed Kab bin Malik some money. One day the latter met the former and demanded his right, and their voices grew very loud. The Prophet passed by them and said, “O Ka’b,” beckoning with his hand as if intending to say, “Deduct half the debts.” So, Kab took half what the other owed him and remitted the other half.