Acts 21:23

Therefore do this which we say to thee: Four men are to us having a vow upon them;

Acts 18:18

And Paul yet having remained sufficient days, having taken leave of the brethren, sailed out to Syria, and with him Priscilla and Aquila; having shorn the head in Cenchrea: for he had a vow.

Numbers 6:2-7

Speak to the sons of Israel, and say to them, When a man or woman shall separate to vow a vow, being consecrated, to be separated to Jehovah:

Treasury of Scripture Knowledge

Summary

Do therefore this that we say to thee: We have four men which have a vow on them;

Bible References

We have

Acts 18:18
And Paul yet having remained sufficient days, having taken leave of the brethren, sailed out to Syria, and with him Priscilla and Aquila; having shorn the head in Cenchrea: for he had a vow.
Numbers 6:2
Speak to the sons of Israel, and say to them, When a man or woman shall separate to vow a vow, being consecrated, to be separated to Jehovah: