A.T. Robertson Commentary Luke 9:5

"And as many as receive you not, when ye depart from that city, shake off the dust from your feet for a testimony against them." — Luke 9:5 (ASV)

As many as receive you not (οσο αν μη δεχωντα υμας). Indefinite relative plural with αν and present middle subjunctive and the negative μη. Here Mt 10:14 has the singular (whosoever) and Mr 6:11 has "whatsoever place."

For a testimony against them (εις μαρτυριον επ' αυτους). Note use of επ' αυτους where Mr 6:11 has simply the dative αυτοις (disadvantage), really the same idea.