Sahih Bukhari Volume 006, Book 060, Hadith Number 175.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 60. Prophetic Commentary on the Qur'an (Tafseer of The Prophet (PBUH))
Narrated By Ibn Abbas : When the Verse: "If there are twenty steadfast amongst you, they will overcome two hundred." (8.65) was revealed, then it became obligatory for the Muslims that one (Muslim) should not flee from ten (non-Muslims). Sufyan (the sub-narrator) once said, "Twenty (Muslims) should not flee before two hundred (non Muslims)." Then there was revealed: 'But now Allah has lightened your (task)...' (8.66)
So it became obligatory that one-hundred (Muslims) should not flee before two hundred (non-muslims). (Once Sufyan said extra, "The Verse: 'Urge the believers to the fight. If there are twenty steadfast amongst you (Muslims)...' was revealed.) Sufyan said, "Ibn Shabrama said, "I see that this order is applicable to the obligation of enjoining good and forbidding evil."