Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) made peace with the people of Najran in exchange for two thousand suits of garments, half of which they would pay to the Muslims in Safar and half in Rajab, and, as a loan, thirty coats of mail, thirty horses, thirty camels and thirty of every type of weapon used in battle; the Muslims are guarantors for them until they return them, if there is a plot (hostilities) in Yemen.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18680