Sahih al-Bukhari 4653
Narrated Ibn `Abbas:
When the Verse:--'If there are twenty steadfast amongst you (Muslims), they will overcome twohundred 
(non-Muslims).' was revealed, it became hard on the Muslims when it became compulsory 
that one Muslim ought not to flee (in war) before ten (non-Muslims). So (Allah) lightened the order by 
revealing: 
'(But) now Allah has lightened your (task) for He knows that there is weakness in you. So if there are 
of you one-hundred steadfast, they will overcome (two-hundred (non-Muslims).' (8.66) So when 
Allah reduced the number of enemies which Muslims should withstand, their patience and 
perseverance against the enemy decreased as much as their task was lightened for them.
حَدَّثَنَا يَحْيَى بْنُ عَبْدِ اللَّهِ السُّلَمِيُّ، أَخْبَرَنَا عَبْدُ اللَّهِ بْنُ الْمُبَارَكِ، أَخْبَرَنَا جَرِيرُ بْنُ حَازِمٍ، قَالَ أَخْبَرَنِي الزُّبَيْرُ بْنُ خِرِّيتٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ لَمَّا نَزَلَتْ ‏{‏إِنْ يَكُنْ مِنْكُمْ عِشْرُونَ صَابِرُونَ يَغْلِبُوا مِائَتَيْنِ‏}‏ شَقَّ ذَلِكَ عَلَى الْمُسْلِمِينَ حِينَ فُرِضَ عَلَيْهِمْ أَنْ لاَ يَفِرَّ وَاحِدٌ مِنْ عَشَرَةٍ، فَجَاءَ التَّخْفِيفُ فَقَالَ رالآنَ خَفَّفَ اللَّهُ عَنْكُمْ وَعَلِمَ أَنَّ فِيكُمْ ضُعْفًا فَإِنْ يَكُنْ مِنْكُمْ مِائَةٌ صَابِرَةٌ يَغْلِبُوا مِائَتَيْنِ‏}‏‏.‏ قَالَ فَلَمَّا خَفَّفَ اللَّهُ عَنْهُمْ مِنَ الْعِدَّةِ نَقَصَ مِنَ الصَّبْرِ بِقَدْرِ مَا خُفِّفَ عَنْهُمْ‏.‏