At the time of Crusades, the term “franks” (ifranj) was common Arabic word for the crusaders. Since that, almost any study of the Crusades from the “Islamic perspective” tends to discover francs in Arab sources. However, medieval Muslim authors mentioned the Franks since the early 9th century, long before the Crusades, but nobody asks when and how Arabic authors actually learn about the Franks. There is still a half-century-old hypothesis by B. Lewis, attributing the word “franc” (faranj) to the Greek “fráŋkos”. The aim of our article is to discover the original source from which the Arabs first learn about the Franks, so we study the 9th-century Arab texts reporting on the first known contact between Arabs and Franks during the Muslim conquest of Spain. It seems that the Arabic faranj could hardly originate from the Greek fráŋkos, as the combination of letters <γκ> sounds as <nk> during this period (which corresponds to another Arabic form firank appearing in a number of texts in 11th–12th centuries and not widely used). That is why the Arabic franc could actually originate from Syriac as a transcription of the Syriac prangāiā. Based on message of the 9th-century historian Ibn Kutaiba we suppose that Arabs learned this term from the Syrian sailors who ensured the crossing of Muslim army through the Strait of Gibraltar in the spring of 711.