Numbers 6:18

‘But if a man dies very suddenly beside him and he defiles the head of hair during his Nazirite vow, then he shall shave his head on the day when he becomes clean; he shall shave it on the seventh day.

And Paul, having remained many days longer, took leave of the brothers and put out to sea for Syria, and with him were Priscilla and Aquila. In Cenchreae he had his hair cut, for he was keeping a vow.

“Therefore do this that we tell you. We have four men who are under a vow;

Now when the seven days were almost over, the Jews from Asia, upon noticing him in the temple, began to throw all the crowd into confusion and laid hands on him,