Reference for Bava Kamma 225:19
ואיכא דמתני אהא נודרין להרגין ולחרמין ולמוכסין שהיא של תרומה שהיא של בית מלך אע"פ שאינה של תרומה אע"פ שאינה של מלך ולמוכסין והאמר שמואל דינא דמלכותא דינא
but is it not a definite transgression to elude the customs? Did Samuel not state that the law of the State is law? — R. Hanina b. Kahana said that Samuel stated that a customs-collector who is bound by no limit [is surely not acting lawfully]. At the School of R. Jannai it was stated that we were dealing here with a customs-collector who acted on his own authority.<span class="x" onmousemove="('comment',' Without the authority of the ruling power. ');"><sup>29</sup></span> Still others read these statements with reference to the following: To [escape] murderers or robbers or customs-collectors one may confirm by a vow a statement that [e.g.] the grain is <i>terumah</i><span class="x" onmousemove="('comment',' V. Glos. ');"><sup>30</sup></span>