Tractate Yadayim - Chapter 4 - Mishnah 3 ידיים פרק ד׳ משנה ג׳

On that day they said: what is the law applying to Ammon and Moab in the seventh year? Rabbi Tarfon decreed tithe for the poor. And Rabbi Elazar ben Azariah decreed second tithe. Rabbi Ishmael said: Elazar ben Azariah, you must produce your proof because you are expressing the stricter view and whoever expresses a stricter view has the burden to produce the proof. Rabbi Elazar ben Azariah said to him: Ishmael, my brother, I have not deviated from the sequence of years, Tarfon, my brother, has deviated from it and the burden is upon him to produce the proof. Rabbi Tarfon answered: Egypt is outside the land of Israel, Ammon and Moab are outside the land of Israel: just as Egypt must give tithe for the poor in the seventh year, so must Ammon and Moab give tithe for the poor in the seventh year. Rabbi Elazar ben Azariah answered: Babylon is outside the land of Israel, Ammon and Moab are outside the land of Israel: just as Babylon must give second tithe in the seventh year, so must Ammon and Moab give second tithe in the seventh year. Rabbi Tarfon said: on Egypt which is near, they imposed tithe for the poor so that the poor of Israel might be supported by it during the seventh year; so on Ammon and Moab which are near, we should impose tithe for the poor so that the poor of Israel may be supported by it during the seventh year. Rabbi Elazar ben Azariah said to him: Behold, you are like one who would benefit them with gain, yet you are really as one who causes them to perish. Would you rob the heavens so that dew or rain should not descend? As it is said, "Will a man rob God? Yet you rob me. But you: How have we robbed You? In tithes and heave-offerings" (Malakhi 3:8). Rabbi Joshua said: Behold, I shall be as one who replies on behalf of Tarfon, my brother, but not in accordance with the substance of his arguments. The law regarding Egypt is a new act and the law regarding Babylon is an old act, and the law which is being argued before us is a new act. A new act should be argued from [another] new act, but a new act should not be argued from an old act. The law regarding Egypt is the act of the elders and the law regarding Babylon is the act of the prophets, and the law which is being argued before us is the act of the elders. Let one act of the elders be argued from [another] act of the elders, but let not an act of the elders be argued from an act of the prophets. The votes were counted and they decided that Ammon and Moab should give tithe for the poor in the seventh year. And when Rabbi Yose ben Durmaskit visited Rabbi Eliezer in Lod he said to him: what new thing did you have in the house of study today? He said to him: their votes were counted and they decided that Ammon and Moab must give tithe for the poor in the seventh year. Rabbi Eliezer wept and said: "The counsel of the Lord is with them that fear him: and his covenant, to make them know it" (Psalms 25:14). Go and tell them: Don't worry about your voting. I received a tradition from Rabbi Yohanan ben Zakkai who heard it from his teacher, and his teacher from his teacher, and so back to a halachah given to Moses from Sinai, that Ammon and Moab must give tithe for the poor in the seventh year.