Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)

Bukhari :: Book 5 :: Volume 59 :: Hadith 321

Narrated Abu Usaid:

On the day of (the battle of) Badr, Allah's Apostle said to us, "When your enemy comes near to you (i.e. overcome you by sheer number), shoot at them but use your arrows sparingly."