^Hammarström, Harald; Forkel, Robert; Haspelmath, Martin; Bank, Sebastian (编). Nkhumbi. Glottolog 2.7. Jena: Max Planck Institute for the Science of Human History. 2016.
^Robert Needham Cust. A Sketch of the Modern Languages of Africa: Accompanied by a Language Map, 第 2 卷. London:Trubner & Co., Ludgale Hill. 1883. 页388.