A.S. Yahuda, Language of the Pentateuch in its Relation to Egyptian [1933], Vol. 1, [1933], 63 That the metaphorical use of 'lip' שפה for 'shore', as e.g. שפת היאור Gen 41, 3; Ex. 2, 3. 7, 15. 'bank of the River Nile' or 'shore of the sea' as in Ex 14, 30, &c. was current also in Egyptian at all times has long been established as e.g. by Ebers, Die Bücher Moses, p. 339. The Egyptians spoke of 'the lip of the water' for the bank of the RIver Nile, thus e.g. Lebensmüde, xv, l. 66 f., p. 42, of the fish 'on the lip of the water' śp.t n mw, on the bank of the Nile.
Yigal Levin: Can anyone explain the word הַצְּפִינוֹ֒ "hacepino" - why is there a dagesh in the sade and not in the pe?
Peter Kirk: See GKC 20h, where (as noted in BDB) this word is listed as an example
of "When a consonant with /Sheva/ is strengthened by /Dagesh forte
dirimens/ to make the /Sheva/ more audible" (spellings of Hebrew points
adjusted).
Uri Hurwitz: This seems a clear mistake of either early MT transmission, or of an early vocalizer. What makes this rather obvious is that in the previous verse, 2:2, in the same root there is a Dagesh Qal in the Pe where it belongs, and no Dagesh in the S(.)ade. The other answer, while possible, is rather forced.
Yitzhak Sapir: Whereas I would like to explain it by comparison with other otherwise unexplained dagesh fortes (as in xami$$im), it appears that the Hiphil had always no vowel after the first verbal stem letter. This can be supported from examples such as EA 256 xi-ix-be-e (=hixbe "hid") as well as verbal stems with the letter n (ngd, nb+, ndx, npl). Even in a case of an absolute suffixed form, the n drops in Jer 27:15. There is no evidence then that there ever was a vowel after the first stem letter as would be required if the dagesh forte ever appeared with the schewa. In contrast, such a situation would require that the p would have a dagesh, like we do not have here. While all this could still be explained as a development of Hebrew, Uri's explanation of a simple error in transmission makes more sense.
Vertaling Bijbel, Kanttekeningen SV, [], Doch als zij hem [6]niet langer verbergen kon, zo nam zij voor hem [7]een kistje van [8]biezen, en belijmde het met lijm en met pek; en zij legde het knechtje daarin, en legde het in de biezen, aan den [9]oever der rivier. 6. Want de Israelieten woonden vermengd onder en met de Egyptenaars, hfdst.3 vs.22. En het bevel van den koning was hard en gevaarlijk het te overtreden, hfdst.1 vs.22; Hebr.11:23. 7. Anders, een lade. 8. Hiervan maakten de Egyptenaars lichte schuiltjes; Jes.18:2. 9. Hebreeuws, lip. Dit deed de moeder, opdat het kind des te lichter zou gehoord, gezien en gevonden kunnen worden.