David (abu Sulaiman) ibn Merwan al-Mukkamas al-Rakki (Arabic: داود إبن مروان المقمص translit.
Harkavy derives his byname from the Arabic "ḳammaṣ" (to leap), interpreting it as referring to his asserted change of faith (Grätz, Gesch.
The publication of Judah Barzilai's commentary to the Sefer Yezirah (Meḳiẓe Nirdamim, 1885), in which is found a poor Hebrew translation of the ninth and tenth chapters of David's philosophical work, first brought the latter into notice.
Pinsker and Grätz, confounding him with Daniel ha-Babli of Cairo, make him a Mohammedan convert to Karaism, on the ground that he is quoted by Karaite scholars, and is called by Hadasi "ger ẓedeḳ" (pious proselyte).
The discovery by Harkavy of the Kitab al-Riyaḍ wal-Ḥada'iḳ, by the Karaite Al-Ḳirḳisani, threw further light on David.
His conversion to Christianity can hardly be reconciled with the fact that he is cited by Baḥya, by Jedaiah Bedersi (in Iggeret Hitnaẓẓelut), and by Moses ibn Ezra.
In one passage David relates that he had a philosophical disputation in Damascus with a Muslim scholar, Shabib al-Baṣri.
Contrary to the practice of Saadia, Bahya, and other Jewish philosophers, he never quotes the Bible, but cites Greek and Arabic authorities.