The Bible mentions the Book of Jasher twice. The Book of Jasher was lost sometime in antiquity, and no mention of it appears in the Dead Sea Scrolls, early Jewish or Christian tradition, or early Rabbinic writings. During the Middle Ages, a time notorious for people passing off newly created works as discovered texts that claimed to be much older, the first version of the Book of Jasher suddenly appeared. Yet, it would not be the only Book of Jasher to see the light of day…
The Biblical Book of Jasher

The Hebrew term for the Book of Jasher is Sefer HaYashar. The Bible mentions the book twice, and possibly a third time. The first instance was when Joshua needed more time to defeat the Amorites:
“And the sun stood still, and the moon stopped, until the nation took vengeance on their enemies. Is this not written in the Book of Jashar? The sun stopped in the midst of heaven and did not hurry to set for about a whole day.” (Joshua 10:13)
The author related a cosmic miracle that saw the sun stand still in the sky for almost a day. Knowing that this account would be questioned, he notes how the Book of Jasher recorded the same event.

The second mention comes from 2 Samuel 1:18. Here, David laments over the king and his friend:
“And David lamented with this lamentation over Saul and Jonathan his son, and he said it should be taught to the people of Judah; behold, it is written in the Book of Jashar. He said: ‘Your glory, O Israel, is slain on your high places! How the mighty have fallen!’” (2 Samuel 1:17-19)
Laments like these often took the form of a song that the nation would sing and teach their children, carrying on the record of what happened for generations. Momentous events in Israelite history would also be celebrated in song, like the song the Israelites sang after crossing the Red Sea and escaping the Egyptian army (Exodus 15:1-21). It is likely that the jaw-dropping event that Joshua 10 recorded would also have been celebrated in song. The Book of Jasher could, therefore, have been a book of songs celebrating significant events and heroes from Israelite history.
In the Septuagint, the Greek translation of the Hebrew Bible, 1 Kings 8:53 ends with the phrase “ἐν βιβλίῳ τῆς ᾠδῆς” (in the book of songs). Assuming the original manuscript(s) it was translated from contained this phrase, which does not appear in the Hebrew manuscripts used to translate the Bible we have today, the Hebrew would be sefer ha-shir, which is close to Sefer HaYashar (Book of Jasher). Some scholars have suggested it may refer to the same book and indicate what it was meant to be.
The Medieval Book of Jasher

The Book of Jasher mentioned in the Bible vanished. For many centuries, if not a couple of millennia, there is no record of its existence. The Dead Sea Scrolls, which held account of and mention a significant number of ancient texts dear to Judaism, make no mention of it, neither does the early Jewish or Christian tradition. The Church Fathers show no knowledge of such a text either.
It was not until the Middle Ages that a work bearing the name the Book of Jasher appeared. Around the 11th to the 12th century CE, a midrash called the Book of Jasher saw the light and it consisted of 91 chapters. It retold the biblical history from the time of Cain to the death of Joshua, adding many details not related to the Biblical narrative.
The author of this work seems to have gathered stories, legends, and traditions that developed around this section of Israelite history and crafted them together in a carefully constructed narrative. He gave it the name the “Book of Jasher” to benefit from the work that the bible considered reliable enough to mention at least twice.

There are ample legitimate reasons to believe this Book of Jasher is not the authentic version referenced in scripture. A common mistake found in later works that claim earlier authorship is the use of names that did not exist at the time the work claims to date to. This is the case with the midrash version of the Book of Jasher when it records that Noah settled in areas that have European names that were given to those areas centuries after the New Testament era.
This version of the Book of Jasher also contradicts the Bible in many places. Here are a few examples:
Abraham’s age when he left Haran:
Jasher 13:5 “… Abram was fifty years old when he went from Haran.”
Genesis 12:4 “… Abram was seventy-five years old when he departed from Haran.”
Who Jacob fled to:
Jasher 29:11 “And Jacob was very much afraid of his brother Esau, and he rose up and fled to the house of Eber the son of Shem…”
Genesis 28:5 “Thus Isaac sent Jacob away. And he went to Paddan-aram, to Laban, the son of Bethuel the Aramean, the brother of Rebekah, Jacob’s and Esau’s mother.”
The number of plagues that struck Egypt:
Jasher 80:2-51 15 plagues mentioned.
Exodus 7-12 mentions 10 plagues.
The Red Sea divided into:
Jasher 81:38 “And the waters of the sea were divided into twelve parts, …”
Exodus 14:22 “And the people of Israel went into the midst of the sea on dry ground, the waters being a wall to them on their right hand and on their left.”

This version of the Book of Jasher also contains narratives that contradict Biblical teaching. For example, Joseph calls on his mother at her grave and she answers him (Jasher 42:30-41). Necromancy is explicitly forbidden in Deuteronomy 18:11-12.
Based on the anachronistic place names, the inconsistencies in detail, and theological challenges, this version of the Book of Jasher cannot be the authentic version the Bible refers to.
Jacob Ilive’s Book of Jasher

Yet another version of the Book of Jasher saw the light in 1751. The historical record shows exactly when and how this version came about. A deist named Jacob Ilive published a Book of Jasher that he claimed was discovered in Gazna and was translated into English from the original Hebrew text. Ilive was known for opposing orthodox Christianity and published pamphlets that challenged it and promoted unorthodox ideas before.
Rabbi Arthur Chiel, in a Journal article titled The Mysterious Book of Jasher (Judaism: A Quarterly Journal, Issue No. 103, Vol. 26,), eloquently shows the purpose of this version. He wrote:
“Ilive’s The Book of Jasher consists of thirty-seven chapters which begin with the Creation story and extend to the rule of ‘Jasher, the son of Caleb who judged Israel in Shiloh.’ Jasher is represented as an adjutant of Moses, along with Joshua. But even a casual reading of this work reveals the book’s real purpose: the rejection of Revelation. Jethro emerges as the ‘founding father’ of Israel’s law code. It is Jethro who convokes Moses and the seventy elders on Mt. Sinai where he instructs them about the governance of Israel. Here, then, was the real intent of The Book of Jasher: to challenge the credibility of the Pentateuch and to diminish altogether the role of Moses.”
In 1756, Ilive was charged and found guilty of fraud related to the claims he made about his version of the Book of Jasher. He was sentenced to three years in prison.
The Book of Jasher: In Conclusion

None of the existing versions of the Book of Jasher can possibly be the original version referenced in the Bible. It seems like the authentic Book of Jasher is, for now at least, lost in the mists of time. Since it is not known when it was lost, it may be that the reason it was not included in the Old Testament canon is that it was lost before that canon was compiled and settled.
There are several other books mentioned in the Old Testament that are also not included in the Bible. They are The Book of the Wars of the Lord (Numbers 21:14), The Book of the Acts of Solomon (1 Kings 11:41), The Book of the Chronicles of the Kings of Israel (1 Kings 14:19), The Book of the Chronicles of the Kings of Judah (1 Kings 15:7), and The Book of the Prophet Iddo (2 Chronicles 13:22). The Book of the Chronicles of the Kings of Israel and The Book of the Chronicles of the Kings of Judah are not the same as 1 and 2 Chronicles.
All the books listed here that have not been included in the canon of the Bible and have been lost though they served as corroboration or gave additional information on what the Old Testament reported. These lost texts were likely official records or historical chronicles.