Merry Christmas! Really nice dagger. Wente-Lukas shows a very similar one, number 298 in her book, which she attributes to the Ndjeny, while mentioning the Daba use similar daggers. In the map of the region, the Ndjeny are shown in the Southern Mandara mountains (and so are the Daba), just north of the Fulbe.
On his site, Wolf-Dieter Miersch shows a couple of similar daggers as Ndjeny/Mafa, and posts a link to a 1910-1912 drawing of such daggers:
http://bildarchiv.frobenius-katalog....rpos=98439.png
Ultimately, your dagger is a really nice, complete example from the early 20th or late 19th century, and it does not get better than that.