Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that when this verse was revealed: "If there are twenty among you who are steadfast, they will overcome two hundred." [Surah al-Anfal: 65] he said: It was made obligatory upon them that one man should not flee from facing ten, nor a group from facing ten times their number. This was hard on the people, so this verse was revealed: "Now Allah has lightened your burden, and He knows that there is weakness in you. So if there are a hundred of you, they will overcome two hundred." [Surah al-Anfal: 66] The narrator said: (They were then ordered) that one man should not flee from facing two, nor a group from facing twice their number.
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: Patience was reduced by as much as the number was lightened.
(b) In the narration of Abdullah bin al-Mubarak (may Allah have mercy on him): It was hard on the Muslims when it was laid down that one should not flee from facing ten, so the command of lightening came. He said: "Now Allah has lightened your burden." [Surah al-Anfal: 66] So when Allah lightened the number for them, patience was reduced in proportion to what He had lightened for them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18080