This Bible contradiction is from the Skeptic's Annotated Bible.
Benjamin had ten sons
Genesis 46:21 View context
And the sons of Benjamin [were] Belah, and Becher, and Ashbel, Gera, and Naaman, Ehi, and Rosh, Muppim, and Huppim, and Ard.
Benjamin had five sons. Two that are sons of Benjamin in Genesis 46 (Ard and Naaman) are grandsons in this list.
Numbers 26:38-40 View context
The sons of Benjamin after their families: of Bela, the family of the Belaites: of Ashbel, the family of the Ashbelites: of Ahiram, the family of the Ahiramites: Of Shupham, the family of the Shuphamites: of Hupham, the family of the Huphamites. And the sons of Bela were Ard and Naaman : of Ard, the family of the Ardites: and of Naaman, the family of the Naamites
Benjamin had three sons
1 Chronicles 7:6 View context
[The sons] of Benjamin; Bela, and Becher, and Jediael, three.
Benjamin had five sons
1 Chronicles 8:1-2 View context
Now Benjamin begat Bela his firstborn, Ashbel the second, and Aharah the third, Nohah the fourth, and Rapha the fifth.