Numbers 25:9 — „And those that died in the plague were twenty and four thousand."
1 Corinthians 10:8 — „Neither let us commit fornication, as some of them committed, and fell in one day three and twenty thousand."
Both records deal with the same event: The plague which came upon God's people when they attached themselves to Baal-Peor and committed adultery (fornication) in that they served idols rather than the true God. 1 Corinthians 10 mentions 23000 of the people which fell in one day. Numbers 25 however speaks of 24000 who lost their lives in that matter. The key to a correct understanding of these two records is again a careful reading and recognizing of some details which are mentioned in these reccords.
Even though both records deal with the same identical event – the plague following Israel's fornication (idol worship) with the Baal-Peor –, they do not refer to the exact same group of people in their mention of these numbers. 1 Corinthians 10:8 mentions 23000, and points out distinctly that these all fell IN ONE DAY. This is the important detail in order to clear up the apparent contradiction between these two records. Number 25:9 mentions 24000 and gives the total number of those who fell because of this plague. The total number of people killed includes the 23000 mentioned in 1 Corinthians 10:8 and in addition some others of the rulers of the people who also lost their lives because of their sin (compare Number 25:4-5). There must have been another 1000 persons who died, but who did not fall in that one day as the 23000. We learn that a total of 24000 people of Israel died at that time, 23000 of them fell in one day.