Sahih Bukhari
Times of the Prayers
Volume: 001 / Book Number: 010 / Hadith Number: 528
Narrated Abu Al-Mahh:
We were with Buraida in a battle on a cloudy day and he said, "Offer the 'Asr prayer early as the Prophet said, "Whoever leaves the 'Asr prayer, all his (good) deeds will be annulled."