This assumption of Friedmann's was subsequently confirmed by the publication of a geonic responsum (A. Harkavy, Teshubot ha-Ge'onim, p. 107, No. 229, Berlin, 1888), where a baraita from the Sifre de-Be Rab to Exodus is quoted, which is the same passage as that cited by Naḥmanides from the Mekilta de-R. Shimon b. Yoḥai, in his commentary on Ex. xxii.