In the ninth century, the Vikings sold tens of thousands of Whites to the Arabs of Spain. According to Michael Woods book In Search of the Dark Ages:
An Arab traveler of the time who came to Spain remarked on the great numbers of European slaves in harems and in the militia. The palace of the Emir of Cordoba in particular had many White girls. Of these unfortunate people the Vikings were undoubtedly a major source of supply.The Arabs in Spain saw the long-term potential of this trade, and as early as the 840s sent a diplomatic mission to Scandinavia to put it on an organized basis.
The most westerly component of the early medieval slave trade in Europe was the British Isles. In the eleventh century the Vikings were active slave traders in Ireland… From Ireland the Vikings took the slaves to be sold in Muslim Spain and Scandinavia, and even to be transported into Russia; some may have been taken as far as Constantinople and the Muslim Middle East… (William Phillips, Slavery from Roman Times to the Early Transatlantic Trade.p. 63).
The Norwegian slave trader was an important enough figure to appear in the 12th century tale of Tristan… Icelandic literature also provides numerous references to raiding in Ireland as a source for slaves.
Norwegian Vikings made slave raids not only against the Irish and Scots (who are often called Irish in Norse sources) but also against Norse settlers in Ireland or the Scottish Isles or even in Norway itself. Slave trading was a major commercial activity of the Viking Age… (Ruth Mazo Karras, Slavery and Society in Medieval Scandinavia, p. 49). The children of White slaves in Iceland were routinely murdered en masse (Karras, p. 52).