Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 320
Narrated Usaid:
On the day of Badr, Allah's Apostle said to us, "When the enemy comes near to you, shoot at them but use your arrows sparingly (so that your arrows should not be wasted)."