It was narrated from 'Abdur-Rahman bin Mas'ud bin Niyar:

"Sahl bin Abi Hathmah came to us when we were in the market and said: "The Messenger of Allah said: When you have estimated, take two-thirds (of the portion you have estimated as Zakah) and leave one-third, and if you do not take (two-thirds) or leave one-third. (One of the reporters) Shu 'bah doubted - leave one quarter."

أَخْبَرَنَا مُحَمَّدُ بْنُ بَشَّارٍ، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، وَمُحَمَّدُ بْنُ جَعْفَرٍ، قَالاَ حَدَّثَنَا شُعْبَةُ، قَالَ سَمِعْتُ خُبَيْبَ بْنَ عَبْدِ الرَّحْمَنِ، يُحَدِّثُ عَنْ عَبْدِ الرَّحْمَنِ بْنِ مَسْعُودِ بْنِ نِيَارٍ، عَنْ سَهْلِ بْنِ أَبِي حَثَمَةَ، قَالَ أَتَانَا وَنَحْنُ فِي السُّوقِ فَقَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏

‏ إِذَا خَرَصْتُمْ فَخُذُوا وَدَعُوا الثُّلُثَ فَإِنْ لَمْ تَأْخُذُوا أَوْ تَدَعُوا الثُّلُثَ - شَكَّ شُعْبَةُ - فَدَعُوا الرُّبُعَ ‏

‏ ‏.‏