Narrated Ibn 'Abbas:
The Messenger of Allah ﷺ conquered Khaibar, and stipulated that all the land, gold and silver would belong to him. The people of Khaibar said: we know the land more than you ; so give it to us on condition that you should have half of the produce and we would have the half. He then gave it to them on that condition. When the time of picking the fruits of the palm-trees came, he sent 'Abd Allah b. Rawahah to them, and he assessed the among of the fruits of the palm-trees. This is what the people of Medina call khars (assessment). He used to say: In these palm-trees there is such-and-such amount (of produce). They would say: You assessed more to us, Ibn Rawahah (than the real amount). He would say: I first take the responsibility of assessing the fruits of the palm-trees and give you half of (the amount) I said. They would say: This is true, and on this (equity) stand the heavens and the earth. We agreed that we should take (the amount which) you said.

حَدَّثَنَا أَيُّوبُ بْنُ مُحَمَّدٍ الرَّقِّيُّ، حَدَّثَنَا عُمَرُ بْنُ أَيُّوبَ، حَدَّثَنَا جَعْفَرُ بْنُ بُرْقَانَ، عَنْ مَيْمُونِ بْنِ مِهْرَانَ، عَنْ مِقْسَمٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ افْتَتَحَ رَسُولُ اللَّهِ ﷺ خَيْبَرَ وَاشْتَرَطَ أَنَّ لَهُ الأَرْضَ وَكُلَّ صَفْرَاءَ وَبَيْضَاءَ . قَالَ أَهْلُ خَيْبَرَ نَحْنُ أَعْلَمُ بِالأَرْضِ مِنْكُمْ فَأَعْطِنَاهَا عَلَى أَنَّ لَكُمْ نِصْفَ الثَّمَرَةِ وَلَنَا نِصْفٌ . فَزَعَمَ أَنَّهُ أَعْطَاهُمْ عَلَى ذَلِكَ فَلَمَّا كَانَ حِينَ يُصْرَمُ النَّخْلُ بَعَثَ إِلَيْهِمْ عَبْدَ اللَّهِ بْنَ رَوَاحَةَ فَحَزَرَ عَلَيْهِمُ النَّخْلَ وَهُوَ الَّذِي يُسَمِّيهِ أَهْلُ الْمَدِينَةِ الْخَرْصَ فَقَالَ فِي ذِهْ كَذَا وَكَذَا قَالُوا أَكْثَرْتَ عَلَيْنَا يَا ابْنَ رَوَاحَةَ . فَقَالَ فَأَنَا أَلِي حَزْرَ النَّخْلِ وَأُعْطِيكُمْ نِصْفَ الَّذِي قُلْتُ . قَالُوا هَذَا الْحَقُّ وَبِهِ تَقُومُ السَّمَاءُ وَالأَرْضُ قَدْ رَضِينَا أَنْ نَأْخُذَهُ بِالَّذِي قُلْتَ .