Leviticus 16:29-31 And this shall be an eternal law for you. Each year on the tenth day of the seventh month you must fast and do no work. This is true of the native born and of the proselyte who comes to join you. This is because on this day you shall have all your sins atoned, so that you will be cleansed. Before God you will be cleansed of your sins. It is a Sabbath of Sabbaths to you, and a day upon which you must fast. This is a law for all time.
From the time that the Israelites left Egypt with a mixed multitude, the mosaic covenant has applied to the proselyte or gentile.
Exodus 12:38
And a mixed multitude went up also with them; and flocks, and herds, even very much cattle.
It was actually at the time when they came back from Babylon than they made a very distinct separation based on blood lines.
Nehemiah 13:3
Now it came to pass, when they had heard the law, that they separated from Israel all the mixed multitude.