Adelard of Bath
Adelard of Bath (; 1080 1152 AD) was a 12th-century English natural philosopher. He is known both for his original works and for translating many important Arabic and Greek scientific works of astrology, astronomy, philosophy and mathematics into Latin from Arabic versions, which were then introduced to Western Europe. He is known as one of the first to introduce the Arabic numeral system to Europe. He stands at the convergence of three intellectual schools: the traditional learning of French schools, the Greek culture of Southern Italy, and the Arabic science of the East.
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: