Acts 21:26
Then Paul took the men, and, on the following day, joining in their vow of abstinence, he entered the temple, and gave notice when the days of abstinence would be completed, at which time an offering should be made for each of them.
Acts 24:18
While engaged in these things, certain Jews from Asia found me fulfilling my vow of abstinence in the temple, not with a multitude, nor with tumult.
Acts 21:24
Take them, and join with them in their vow of abstinence, and pay their expenses, in order that they may shave their heads; and all will know that the things which they have heard reported of you are nothing; but that you yourself also walk orderly, and keep the law.
1 Corinthians 9:20
And to the Jews, I became as a Jew, that I might gain the Jews: to those who are under law, as under law, (not being myself under law,) that I might gain those who are under law;