Matthew 10:14

And whosoever shall not receive you, nor hear your words, as ye go forth out of that house or that city, shake off the dust of your feet.

The Jewish rabbis taught that the dust of heathen cities defiled, and the symbolical action of shaking off the dust of the feet indicated that any person or city rejecting the apostles' words was no better than the heathen. Paul and Barnabas, on their first missionary journey, were rejected by the Jews and certain women of honorable estate, "But they shook off the dust of their feet against them, and came unto Iconium" (Acts 13:51). This shows that the custom here initiated by Jesus was continued after the church was established.