וַיְהִ֗י הֵ֚ם מְרִיקִ֣ים שַׂקֵּיהֶ֔ם וְהִנֵּה־אִ֥ישׁ צְרוֹר־כַּסְפּ֖וֹ בְּשַׂקּ֑וֹ וַיִּרְא֞וּ אֶת־צְרֹר֧וֹת כַּסְפֵּיהֶ֛ם הֵ֥מָּה וַאֲבִיהֶ֖ם וַיִּירָֽאוּ׃
Ora, mentr’essi vuotavano i loro sacchi, ciascheduno trovò il gruppo del proprio denaro nel suo sacco; ed essi ed il loro padre, al vedere i loro gruppi di denaro, s’impaurirono.
Rashbam on Genesis
כספיהם, seeing that the letter ס in the word כספיהם “swallows” the otherwise necessary chataf patach under it, the letter פ, normally weak, without the dagesh, has been given a dagesh in this instance. A similar example of this construction is found in the relationship of נסך, nessech, and נסכיהם, nisskeyhem.
Radak on Genesis
בשקו, in the actual text it does not say בפי שקו, as we already mentioned on verse 27.