Ibn Faḍlān (d. 960), Risāla

وهم أوحش الناس كلاماً وطبعاً كلامهم أَشبه شيء بصياح الزرازير وبها قرية على يوم يقال لها أَردكو أَهلها يقال لهم أُلكردلية كلامهم أَشبه شيءٍ بنقيق الضفادع

“[The Khwarizmians] are the most barbarous of people, both in speech and customs. Their language sounds like the cries of starlings. In their country there is a village one day’s journey away called Ardakuwa, whose inhabitants are known as Kardaliyya, and their speech sounds like the croaking of frogs.”

What Ibn Faḍlān gives as Ardakuwa (اردكو) may refer to the town al-Maqdisi calls Ardh-Khiva, located to the southeast of the main settlement of Kath (or may not; I haven’t seen it explained anywhere, though). That the inhabitants of this Ardakuwa should be called “Kardaliyya” is not clear—perhaps Ibn Faḍlān combined here reference to inhabitants of a different town, Kurdar, in the northeast of Khwarizm?

Source: Ibn Faḍlān, Risālat Ibn Faḍlān, edited by Sāmī Dahhān (Damascus, 1959), p. 82

Ibn Ḥawqal (d. ca. 978), Kitāb ṣūrat al-arḍ

وهم أكثر أهل خراسان انتشارا وسفرا، وليس بخراسان مدينة [كبيرة] إلّا وفيها من أهل خوارزم جمع كثير، ولسان أهلها مفرد بلغتهم وليس بخراسان لسان على لغتهم

"[the Khwarizmians] are the most widespread and widely-traveld people of Khurāsān, and there is no city in Khurāsān that does not have a large group of Khwarizmians, and their language is unique to them, no other like it is spoken in Khurāsān"

Source: Ibn Ḥawqal, Kitāb ṣūrat al-arḍ, edited by J. H. Kramer (Leiden, 1938), vol. 2, pp. 477–478, 481–482.

al-Maqdisī (d. 991), Aḥsan al-taqāsīm fī ma‘rifat al-aqālīm

لسان اهل خوارزم لا يُفهم
“The language of the people of Khwarizm cannot be understood”

In other words, Chorasmian was to al-Maqdisī not similar to Persian, many different varieties of which he mentions in his work.

Source: Basil Anthony Collins, translator, The Best Divisions for Knowledge of the Regions (Reading, 1994), p. 272; ed. M. F. de Goeje, Bibliotheca Geographorum Arabicorum, Vol. 3, (Leiden, 1877, rev. 1906)