Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) made a peace treaty with the people of Najran for two thousand garments. In the aforementioned hadith it says: "Their places of worship shall not be demolished, no priest of theirs shall be expelled, and they shall not be turned away from their religion, as long as they do not introduce something new or consume usury (riba)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18715