Khubayb ibn Abdur Rahman reported having heard Abdur Rahman ibn Mas’ud ibn Niyar say that Sahi ibn Abu Hathmah came to them and narrated that Allah’s Messenger (SAW) said, ‘When you have made an estimate, leave one third aside, and if you do not leave aside the third then leave aside (at least) a fourth (that is, exempt from akah).”
[Ahmed15713, Abu Dawud 1605]