Acts 21:26
Then Paul took the men and the next day he observed the ceremony of purification with them. Then he went into the Temple, declaring [to the priest] when he would fulfill the [required] days of the purification [ceremony] and [be ready] for the sacrifices to be offered for each of them.
Acts 24:18
While doing this, they [i.e., the Jews] found out that I had undergone the rites of purification in the Temple. There was no crowd and no commotion. But certain Jews from [the province of] Asia
Acts 21:24
Take these men and observe the ceremony of purification with them, pay their expenses so they can shave their heads [i.e., to signify that they are making a vow] and [then] everyone will know that there is no truth in what people have been told about you, but that you, too, are living properly and observing the law of Moses.
1 Corinthians 9:20
I behaved like a Jew in front of the Jews in order to win Jews [to Christ]. I behaved like a person who was under [obligation to observe] the law [i.e., Jews] in front of those who observe that law, although I was not [really] under [obligation to] it. I did this to win those who are under [obligation to observe] the law.