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.
Islamic world contributions to Medieval Europe
The translation of Al-Khwarizmi's work greatly influenced mathematics in Europe. As Professor Victor J. Katz writes: "Most early algebra works in Europe in fact recognized that the first algebra works in that continent were translations of the work of al-Khwärizmï and other Islamic authors. There was also some awareness that much of plane and spherical trigonometry could be attributed to Islamic authors". The words algorithm, deriving from Al-Khwarizmi's Latinized name Algorismi, and algebra, deriving from the title of his AD 820 book "Hisab al-jabr w’al-muqabala, Kitab al-Jabr wa-l-Muqabala" are themselves Arabic loanwords. This and other Arabic astronomical and mathematical works, such as those by al-Battani and Muhammad al-Fazari's "Great Sindhind" (based on the "Surya Siddhanta" and the works of Brahmagupta). were translated into Latin during the 12th century.