Yes, there is such a passage:
Hosea 2:23 ...I will have compassion on her on whom compassion was not had, and I will say to a people that was not my people: Thou art my people, and they: Thou art my God.
Israel cannot be "her on whom compassion was not had," since God called Abraham from idolatry to be sons of the living God and showered them with mercy above any nation; and from the rest of Scripture we know who "My People" refers to, namely, "Israel:"
2 Samuel 7:10 And I will appoint a place for my people Israel, and will plant them, and they shall dwell therein, and shall not be disturbed any more, neither shall the children of iniquity afflict them any more, as they did before.
So we see that God explicitly says that another people shall Israel shall be called His people, and that, therefore, they will say of Him, "Thou art my God."
But this isn't so shocking or sandalous, since converts to Judaism from other nations were existent, very much so, and therefore considered as much a part of Israel as anyone else: there was a very real conception of non-Jews by birth being capable of becoming Jews by circumcision, that is, of converts to the Jewish faith.
Judith 14:6 Then Achior seeing the power that the God of Israel had wrought, leaving the religion of the gentiles, he believed God, and circumcised the flesh of his foreskin, and was joined to the people of Israel, with all the succession of his kindred until this present day.
And of course there was the belief among the Maccabees that uncircumcised state of even uncircumcised Jewish children was 'heathenish,' and needed corrected as part of the crusade for restoring the tradition and orthodoxy to the Hellenized Jews:
1 Maccabees 2:46 And they circumcised all the children whom they found in the confines of Israel that were uncircumcised: and they did valiantly.
Moreover, God selected the Israelite people to be a light to the Gentiles, that is, the leaders and showers of the way, not the sole beneficiaries of the way:
Isaiah 49:6 And he said: It is a small thing that thou shouldst be my servant to raise up the tribes of Jacob, and to convert the dregs of Israel. Behold, I have given thee to be the light of the Gentiles, that thou mayst be my salvation even to the farthest part of the earth.
God chose Israel, but His sights were to all mankind, with Israel at the helm, showing the way, exemplifying the grace God grants to sinners, and showing the excellence of keeping His law, and the fruits thereof. The salvation and mercy He had on Israel was intended for all men, but He needed to form a people who were fully His first, in order to show that this is possible, admirable, and that in the very act of choosing a people among infinitudes of people, that it was all by the mercy of God: since He didn't choose Israel for its greatness: this is how the mercifulness of God is shown in choosing a special people to be a light to the Gentiles.