Abu Dawud Book 17, Hadith Number 3559.
Chapter : Not known.
Narated By Ya’la ibn Umayyah : The Apostle of Allah (PBUH) said to me: When my messengers come to you, give them thirty coats of mail, and thirty camels. I asked: Apostle of Allah, is it a loan with a guarantee of its return, or a loan to be paid back? He replied : It is a loan to be paid back.