Numerical digit
From India, the thriving trade between Islamic sultans and Africa carried the concept to Cairo. Arabic mathematicians extended the system to include decimal fractions, and Muḥammad ibn Mūsā al-Ḵwārizmī wrote an important work about it in the 9th  century. The modern Arabic numerals were introduced to Europe with the translation of this work in the 12th century in Spain and Leonardo of Pisa's "Liber Abaci" of 1201. In Europe, the complete Indian system with the zero was derived from the Arabs in the 12th century.
History of the Hindu–Arabic numeral system
The work was most likely to have been Brahmagupta's "Brahma Sphuta Siddhanta" (Ifrah)  (The Opening of the Universe) which was written in 628 . Irrespective of whether Ifrah is right, since all Indian texts after Aryabhata's "Aryabhatiya" used the Indian number system, certainly from this time the Arabs had a translation of a text written in the Indian number system. 
In his text "The Arithmetic of Al-Uqlîdisî" (Dordrecht: D. Reidel, 1978), A.S. Saidan's studies were unable to answer in full how the numerals reached the Arab world: