This is a sampling of numerous contemporary references to the practice of rabbinical Judaism among the Khazars:
"For in the lands of Gog and Magog who are a Hunnish race and call
themselves Gazari there is one tribe, a very belligerent one -
Alexander enclosed them and they escaped - and all of them profess
the Jewish faith."
- written by Christian Druthmar in 864
"The Khazars and their king are all Jews."
- written by Ahmad Ibn Fadlan circa 921/922
"All of the Khazars are Jews. But they have been Judaized
recently."
- written by Ibn al-Faqih, circa 930
"After those days there arose from the sons of Khazar kagan Bulan
a king, Obadiah by name. He was an upright and just man. He
reorganized the kingdom and established the Jewish religion properly
and correctly. He built synagogues and schools, brought in many
Israelite sages, honored them with silver and gold, and they
explained to him the 24 Books of the Bible, Mishnah, Talmud, and the
order of prayers established by the Khazzans. He was a man who feared
God and loved the law and the commandments."
- written by Khazar King Joseph in his Reply to Hisdai ibn Shaprut in
955
"The Khazar king and his vizier travelled to the deserted
mountains on the seashore, and arrived one night at the cave in which
some Jews used to celebrate the Sabbath. They disclosed their
identity to them, embraced their religion, were circumcized in the
cave, and then returned to their country, eager to learn the Jewish
law. They kept their conversion secret, however, until they found an
opportunity of disclosing the fact gradually to a few of their
special friends. When the number had increased, they made the affair
public, and induced the rest of the Khazars to embrace the Jewish
faith. They sent to various countries for scholars and books, and
studied the Torah. Their chronicles also tell of their prosperity,
how they beat their foes, conquered their lands, secured great
treasures, how their army swelled to hundreds of thousands, how they
loved their faith, and fostered such love for the Holy House that
they erected a Tabernacle in the shape of that built by Moses."
- written by Judah Halevi of Toledo, Spain in "The Book of the
Khazars" in 1140
"You will find the communities of Israel spread abroad... as far
as Dailam and the river Itil where live Khazar peoples who became
proselytes. The Khazar king Joseph sent a letter to Hisdai
ibn-Shaprut and informed him that he and all his people followed the
rabbinical faith. We have seen descendants of the Khazars in Toledo,
Pupils of the Wise, and they have told us that the remnant of them is
of the rabbinical belief."
- written by Abraham ibn Daud of Toledo, Spain in "The Book of
Tradition" in 1161
"Ibn-al-Athir tells how in the days of Harun, the emperor of
Byzantium forced the Jews to emigrate. They came to the Khazar
country, where they found an intelligent but untutored race and
offered them their religion. The inhabitants found it better than
their own and accepted it."
- written by Dimashqi in 1327