Sahl bin Abi Hathmah (RAA) narrated, “We were commanded by the Messenger of Allah (ﷺ), ‘Whenever you assess the amount of something, estimate the [Zakah] and ignore one-third. If you do not, then leave (at least) one fourth.” Related by the five Imams, except for Ibn Majah.

وَعَنْ سَهْلِ بْنِ أَبِي حَثْمَةَ ‏-رَضِيَ اَللَّهُ عَنْهُمَا‏- قَالَ: أَمَرَنَا رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ إِذَا خَرَصْتُمْ, فَخُذُوا, وَدَعُوا اَلثُّلُثَ, فَإِنْ لَمْ تَدَعُوا اَلثُّلُثَ, فَدَعُوا اَلرُّبُعَ } رَوَاهُ اَلْخَمْسَةُ إِلَّا اِبْنَ مَاجَهْ, وَصَحَّحَهُ اِبْنُ حِبَّانَ, وَالْحَاكِم ُ [1]‏ .‏