Nombres 26:13

From Zerach. This was Tzochar, meaning the same as “Tzohar,” illumination. However, the family of Ohad became extinct. Also, five [families] of the tribe of Binyamin, as he had descended to Egypt with ten sons, yet here only five are counted. Also, Etzbon, of Gad — so there are seven families. I found, in the Talmud Yerushalmi, that when Aharon died the clouds of glory departed, and the Canaanites came to wage war against Israel. They (Bnei Yisroel) resolved to return to Egypt, and went back eight journeys, from Mount Hor to Moserah, as it is said, “Bnei Yisroel journeyed from Be’eros Bnei Yaakon to Moserah, where Aharon died.” Now did he not die at Mount Hor? And from Moserah to Mount Hor there are eight journeys going back. But, they returned, and the Levites pursued them to bring them back, killing seven of their families. And four Levite families fell; The families of Shim’i and Uzieli. Of the sons of Yitzhar, none are counted here, except for the Korachite family. I do not know the identity of the fourth. R’ Tanchuma expounded, that they died in the plague at the affair of Bil’am — however, according to the loss suffered by the tribe of Shimon in this counting, as compared with the first counting at the Sinai desert, it appears that all twenty four thousand fell from the tribe of Shimon.

Of Zerach, the family of Zerach; of Shaul, the family of Shaul.

L’ZERACH’ (OF ZERAH). “He is [identical with] ‘Tzochar’ [Zohar — mentioned in Genesis 46: 10 as one of the sons of Simeon who went down to Egypt], and it [the name Zerach (Zerah)] is an expression meaning tzohar [‘shining,’ which is also the meaning of Zerach]. But the family of Ohad [the other son of Simeon mentioned ibid., in Genesis] became extinct. Similarly five families of the tribe of Benjamin [had by now ceased to exist], for he [Benjamin] went down to Egypt with ten sons, and here Scripture only counts five.” This is Rashi’s language.
And Rashi has furthermore written: “All the families were called by the names of those [of their ancestors] who went down to Egypt, but those who were born after that time were not called families [in their own right and their own names], except for the families of Ephraim and Menasheh, both of whom were born in Egypt, and Ard and Naaman, the sons of Bela the son of Benjamin. who went down to Egypt, and here in Verse 40 they are referred to as sons of Bela, who was himself a son of Benjamin, we must perforce say that the ones referred to here were not the same as those mentioned there [but had the same names]. Furthermore we must perforce say that the Ard and Naaman mentioned here were not amongst those who went down to Egypt, for otherwise Scripture would have mentioned them there in Genesis, in the same way that it counts the grandchildren of Judah and Asher. This is the meaning of Rashi when he wrote: “except for the families of Ephraim and Menasheh, both of whom were born in Egypt, and Ard and Naaman, the sons of Bela the son of Benjamin.” However, the question then arises: why are Ard and Naaman, the sons of Bela, counted here, since they were not amongst those who went down to Egypt? In other words, why were they an exception to the rule? To answer this question Rashi quotes the statement which he found in the work of Rabbi Moshe the Preacher. And I have found [it written] in the work of Rabbi Moshe the Preacher, Note 146. that their mother [that of Ard and Naaman — i.e., the wife of Bela] went down to Egypt when she was already pregnant with them [and therefore they formed separate families, since they are also included amongst ‘those who went down’ to Egypt]. Now if this is a tradition, well and good. But if not, I say that Bela had many children, but from each of these two, Ard and Naaman, there came forth a large family, [and therefore they formed …