Midrash su Esdra 6:12

What did Ezra, Zerubbabel, and Jeshua do? First, they summoned the entire community to the House of the Lord. They brought there three hundred priests, three hundred books of the law, three hundred shofars, and three hundred children. The children blew the shofars, and the Levites chanted and sang. After that, they proclaimed the ban, the curse, and the excommunication against the Samaritans with the secret of the ineffable Name and the writing used on the tablets (of the Decalogue), and the excommunication of the heavenly and earthly courts, so that no Israelite would henceforth eat the bread of a Cuthite. As a result of this episode, our sages said that anyone who ate the bread of a Cuthite would be considered as eating the meat of a pig, and that no Cuthite could be admitted into the ranks of Israel, nor could they participate in the resurrection of the dead, as it is said: It is not for you, but for us, to build the house of God (Ezra 4:3), And ye have no portion, no right, no memorial in Jerusalem (Neh. 2:20). They wrote out the ban, sealed it, and sent it to the Israelites who were in Babylon, and these added other decrees against them. King Cyrus also established an everlasting ban against them, as it is said: May the God who has caused His name to dwell there overthrow all kings and peoples that shall put forth their hand to alter the same (Ezra 6:12).

They sent the ban (letter) to the Israelites who were in Babylon. Moreover, they added an additional ban upon them, and King Cyrus ordained it as a perpetual ban upon them, (as it is said,) "And the God that hath caused his name to dwell there overthrow all kings and peoples that shall put forth their hand to alter the same, to destroy this house of God which is at Jerusalem. I, Darius, have made a decree; let it be done with all diligence" (Ezra 6:12).