Abu Dawud Book 3, Hadith Number 1601.
Chapter : Not known.
Narated By Sahl ibn AbuHathmah : AbdurRahman ibn Mas’ud said: Sahl ibn AbuHathmah came to our gathering. He said: The Apostle of Allah (PBUH) commanding us said: When you estimate take them leaving a third, and if you do not leave or find a third, leave a quarter.