**Yes, there were -- and vice versa**. There were European (Christian knights) operating as mercenaries for Muslim rulers **as well as** Muslim knights/mercenaries in Christian courts. ---------- ***[Farfanes][1]* - Christian Knights as Mercenaries (for Muslim Rulers)** Mainly in the Maghreb but it was not ad-hoc. In other words, it was institutionalised - *emphasis mine*: >***In the medieval period, Muslim rulers frequently hired Christian mercenary soldiers to defend their persons and bolster their armies***. Nowhere was this practice more common than ***in North Africa***, a region, then as now, linked to Europe through migration, diplomacy, and trade. From the twelfth century to the sixteenth, North African regimes of all types found it useful to recruit European fighters to their sides. Some of these mercenaries were former prisoners of war, while others were prominent political exiles. Most, though, were of humbler origin, fighting men who found a lively market for their services in the decentralized, fiercely competitive political environment of the late medieval Maghrib. >Though their terms of service were informal at first, by the thirteenth century Christian mercenaries were a well-defined presence in North Africa. Treaties negotiated between their homelands and ***the governments that hired them specified their wages, weapons, and supplies in minute detail***. source: ***[The Papacy and Christian Mercenaries of Thirteenth-Century North Africa][2]***, Speculum (Volume 89, Number 3 | July 2014), p. 601. *It wasn't just captured soldiers as slaves but also voluntary service* - same source, p. 607: >Christian mercenaries had first come to the Maghrib a hundred years before. Many of them were prisoners of war captured by the Almoravids during their Iberian campaigns. ***These conscripts were soon joined by genuine volunteers***, the most famous of whom was ***[Reverter][3]***, viscount of Barcelona and lord of La Guardia de Montserrat, who rose to a leadership position in the Almoravid army before dying in the Maghrib in 1144. ---------- **Muslim Knights under Christian Kings** Not what was asked specifically, but just for context (and perhaps a better understanding of Medieval history) - *emphasis mine*: >Sometime in April 1285, five Muslim horsemen crossed from the Islamic kingdom of Granada into the realms of the Christian Crown of Aragon to meet with the king of Aragon, who showered them with gifts, including sumptuous cloth and decorative saddles, for agreeing to enter the Crown’s service. >They were not the first or only Muslim soldiers to do so. Over the course of the thirteenth and fourteenth centuries, the ***Christian kings of Aragon recruited thousands of foreign Muslim soldiers to serve in their armies and as members of their royal courts.*** Based on extensive research in Arabic, Latin, and Romance sources, The Mercenary Mediterranean explores this little-known and misunderstood history. Far from marking the triumph of toleration, Hussein Fancy argues, the alliance of Christian kings and Muslim soldiers depended on and reproduced ideas of religious difference. ***Their shared history represents a unique opportunity to reconsider the relation of medieval religion to politics, and to demonstrate how modern assumptions about this relationship have impeded our understanding of both past and present***. source: ***[The Mercenary Mediterranean][4]*** (Chicago University Press, 2016) I have read (not in history SE) that Muslim soldiers should not be considered 'knights' because they lacked a ***[chivalric code.][5]***. It has mostly been assumed that ***[Saladin's exemplary conduct][6]*** was an anamoly. If there is hesitation to consider Muslim soldiers as Knights, have a look at ***[Furusiyya][7]*** and ***[Mubarizun][8]***. [1]: https://en.wikipedia.org/wiki/Farfanes [2]: http://www.journals.uchicago.edu/doi/abs/10.1017/S0038713414000761 [3]: https://en.wikipedia.org/wiki/Reverter_de_La_Guardia [4]: http://press.uchicago.edu/ucp/books/book/chicago/M/bo22776804.html [5]: https://en.wikipedia.org/wiki/Chivalry [6]: https://books.google.com.my/books?id=RzbCgQBhNI4C&pg=PT316&lpg=PT316&dq=Saladin%27s%20exemplary%20conduct&source=bl&ots=hzDVlwW5MG&sig=A8EsbAUellcS86KGCytTk6qYDHs&hl=en&sa=X&redir_esc=y#v=onepage&q=Saladin's%20exemplary%20conduct&f=false [7]: https://en.wikipedia.org/wiki/Furusiyya [8]: https://en.wikipedia.org/wiki/Mubarizun