Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 437
Narrated 'Ali:
On the day of Al-Khandaq (i.e. Trench), the Prophet said '(Let) Allah fill their (i.e. the infidels') houses and graves with fire just as they have prevented us from offering the Middle Prayer (i.e. 'Asr prayer) till the sun had set."