Commercial Transactions (Kitab Al-Buyu)
Dawud :: Book 22 : Hadith 3351
Narrated Abdullah ibn Amr ibn al-'As:
The Apostle of Allah (peace_be_upon_him) commanded him to equip an army, but the camels were insufficient. So he commanded him to keep back the young camels of sadaqah, and he was taking a camel to be replaced by two when the camels of sadaqah came.