Sunnan Abu Dawud Collection: ::Book Number 19:: Hadith # 3035
Narrated Abdullah ibn Abbas: The Apostle of Allah (peace_be_upon_him) concluded peace with the people of Najran on condition that they would pay to Muslims two thousand suits of garments, half of Safar, and the rest in Rajab, and they would lend (Muslims) thirty coats of mail, thirty horses, thirty camels, and thirty weapons of each type used in battle. Muslims will stand surely for them until they return them in case there is any plot or treachery in the Yemen. No church of theirs will be demolished and no clergyman of theirs will be turned out. There will be no interruption in their religion until they bring something new or take usury. Isma'il said: They took usury.