Al-Sha'bi (may Allah have mercy on him) said that Khalid bin al-Walid (may Allah be pleased with him) made a treaty with (the people of) al-Hirah and the people of Ayn al-Tamr, and wrote to Sayyiduna Abu Bakr (may Allah be pleased with him), who approved it. Yahya said: I said to al-Hasan bin Salih (may Allah have mercy on him): So the people of Ayn al-Tamr are like the people of al-Hirah: something is due from them, but nothing is due on their land? He said: Yes.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18361