Jerome
Catena Aurea · Matthäusevangelium 10
And into whatsoever city or town ye shall enter, enquire who in it is worthy; and there abide till ye go thence. And when ye come into an house, salute it. And if the house be worthy, let your peace eome upon it: but if it be not worthy, let your peace return to you. And whosoever shall not receive you, nor hear your words, when ye depart out of that house or eity, shake off the dust of your feet. Verily I say unto you, It shall be more tolerable for the land of Sodom and Gomorrha in the day of judgment, than for that city.
Also they shake off the dust as a testimony of the Apostles’ toil, that in preaching the Gospel they had come even so far, or as a token that from those that rejected the Gospel they would accept nothing, not even the necessaries of life.