Some of the Jews bound themselves — Such execrable vows were not uncommon among the Jews. And if they were prevented from accomplishing what they had vowed, it was an easy matter to obtain absolution from their rabbis.
Related Commentaries of Acts 23:12
Acts 23:12
12 And when it was day, certain of the Jews banded together, and bound themselves under a curse,a saying that they would neither eat nor drink till they had killed Paul.