C. F. Keil and Franz Delitzsch on Job 42:13

Job 42:13 13  And he had seven sons and three daughters.

Therefore, instead of the seven sons and three daughters which he had, he receives just the same again, which is also so far a doubling, as deceased children also, according to the Old Testament view, are not absolutely lost, 2Sa 12:23. The author of this book, in everything to the most minute thing consistent, here gives us to understand that with men who die and depart from us the relation is different from that with things which we have lost. The pausal שׁבענה (instead of שׁבעה), with paragogic âna, which otherwise is a fem. suff. (Ges. §91, rem. 2), here, however, standing in a prominent position, is an embellishment somewhat violently brought over from the style of the primeval histories (Gen 21:29; Rth 1:19): a septiad of sons. The names of the sons are passed over in silence, but those of the daughters are designedly given.