Sahih Bukhari Volume 5, Book 59, Hadith Number 437.

Narrated By ‘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.”