Charles Ellicott Commentary Numbers 25:9

"And those that died by the plague were twenty and four thousand." — Numbers 25:9 (ASV)

Twenty and four thousand.— In 1 Corinthians 10:8 the number of those who fell in one day is said to have been three and twenty thousand. It has been supposed that a thousand were put to death by the judges, and that these were not included in St. Paul’s enumeration. Presuming, however, that there has been no error in either place on the part of the scribes in recording the numbers, the words in one day may account for the apparent discrepancy.