Halakha Maleakhi 3:3: Mishneh Torah, Kings and Wars

During the days of King Messiah, when he will be secure in his monarchy, and all of Israel will gather about him, everyone’s genealogy will be clarified by him by means of the Holy Spirit which will rest upon him, as it says, “And he shall sit as a purifier and refiner…” (Malachi 3:3). The Sons of Levi will be the first to be purified¹⁴⁵Their lineage will be determined first., and he will say, “this one has the pedigree of a Kohen, and this one has the pedigree of a Levite”. He will reject those who have no (true) lineage¹⁴⁶As Levites and Kohanim. and make them Israelites, as it says, “And the Tirashoso said to them…until a Kohen will arise with the Urim and Tumim” (Ezra 2:63). You have now learned that those with a pedigree will be confirmed, and lineage will be made known, by means of the Holy Spirit. He will not ascertain the ancestry of Israel except regarding which tribe they are from, and inform us that this one is from such and such a tribe and that one is from such and such a tribe. But, he will not tell us whether someone presumed of legitimate pedigree is a bastard or a slave. For the Law is that the family which had someone assimilate within it, assimilates him¹⁴⁷Lit., “the family which became assimilated, assimilates.” The commentary in the Rambam La’am says “remains in its presumption of legitimate lineage”..