When the verse "If there are twenty steadfast among you, they will overcome two hundred" [Anfal 8:65] was revealed, it was made binding upon them that twenty must not flee from two hundred, and that one must not flee from ten.Then Allah said, "Now Allah has lightened your burden, for He knows that there is weakness in you. So if there are a hundred steadfast among you, they will overcome two hundred" [Anfal 8:66]. So it was made binding upon them that one must not flee from two, and a hundred must not flee from two hundred. But if a man flees from three, he has not counted as having fled.
لما نزلت: {إن يكن منكم عشرون صبرون يغلبوا مائتين}، فكتب عليهم أن لا يفر عشرون من المائتين، ولا يفر واحد من عشرة، ثم قال: {الآن خفف الله عنكم وعلم أن فيكم ضعفا فإن يكن منكم مائة صابرة يغلبوا مائتين} فكتب عليهم أن لا يفر واحد من اثنين ومائة من المائتين، فان فر من ثلاثة فلم يفر.
Ibn Abu Hatim reported it in his Tafsir (5/9138) from Muhammad bin Abdullah bin Yazid Muqri and Yunus bin Abdul-Ala Misri, the wording being Ibn Muqri's, who both said, Sufyan narrated to us, from Amr bin Dinar, from Ibn Abbas, who said, then he mentioned it. Its chain of transmission is sahih.