Ambrose of Milan
Catena Aurea · Lukasevangelium 9
Then he called his twelve disciples together, and gave them power and authority over all devils, and to cure diseases. And he sent them to preach the kingdom of God, and to heal the sick. And he said unto them, Take nothing for your journey, neither staves, nor scrip, neither bread, neither money; neither have two coats apiece. And whatsoever house ye enter into, there abide, and thence depart. And whosoever will not receive you, when ye go out of that city, shake off the very dust from your feet for a testimony against them. And they departed, and went through the towns, preaching the Gospel, and healing every where.
He pronounces it to be foreign to the character of a preacher of the heavenly kingdom to run from house to house and change the rights of inviolable hospitality; but as the grace of hospitality is supposed to be offered, so also if they are not received the dust must be shaken off, and they are commanded to depart from the city; as it follows, And whosoever will not receive you when ye go out of that city, shake off the very dust from your feet for a testimony, &c.