Acts 21:26
Then Paul took the men, and the next day purifying himself with them entered into the temple, to signify the accomplishment of the days of purification, until that an offering should be offered for every one of them.
Cross-reference
In Acts 21:24, the elders instruct Paul to undergo purification; here he carries out that command, showing his willingness to live in observance of the law.
Acts 24:18 references the same purification event, providing Paul's own account of being found purified in the temple without disturbance.
In Acts 24:17, Paul explains he came to bring alms and offerings—the very purpose behind the purification rite he undertakes here.
In Acts 24:11, Paul later states it was only twelve days since he went to worship—providing the timeline for this temple visit and purification.
Numbers 6:13-20 describes the Nazirite vow completion ritual, providing the OT background for the purification and offerings Paul performed.
1 Corinthians 9:20 explains Paul's method of becoming a Jew to win Jews, which he exemplifies in Acts 21:26 by undergoing purification.