Tosefta zu Jeschijahu 10:78

On that very day stood Judah, an Ammonite convert, before them in the study hall. He said to them, "May I come into the community?" Rabban Gamaliel said to him, "You are forbidden!" Rabbi Yehoshua said to him, "But are the Ammonites and Moabites still in their place? Look, Sennacherib already arose and mingled all the nations, as written (Isaiah 10:13) 'I have erased the borders of peoples, and plundered their treasures!'" Rabban Gamaliel said to him, "But wasn't it already said, (Jeremiah 49:6) 'And after that I will return the exile of the Ammonites, declares the LORD!'? First in Judah He said, have they still not returned?" He said to him, "The verse says, (Amos 9:14) 'And I will return the exile of My people Israel.' In the same way that they [the northern tribes[ have not already returned, so too they [the Ammonites] have not returned." Judah the Ammonite convert said to them, "What am I to do?" They said to him, "You have already heard from the mouth of the elders: behold, you are permitted to come into the community!" Rabban Gamaliel said to him, "Even an Egyptian! Similarly the verse said that God would give to Egypt an allotment, as written, (Ezekiel 29:13) 'After forty years I will gather Egypt from the peoples to which they were scattered, and they will return to their land.'"