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(יג) וַיִּדֹּם הַשֶּׁמֶשׁ וְיָרֵחַ עָמָד עַד יִקֹּם גּוֹי אֹיְבָיו הֲלֹא הִיא כְתוּבָה עַל סֵפֶר הַיָּשָׁר וַיַּעֲמֹד הַשֶּׁמֶשׁ בַּחֲצִי הַשָּׁמַיִם וְלֹא אָץ לָבוֹא כְּיוֹם תָּמִים.
(יז) וַיְקֹנֵן דָּוִד אֶת הַקִּינָה הַזֹּאת עַל שָׁאוּל וְעַל יְהוֹנָתָן בְּנוֹ. (יח) וַיֹּאמֶר לְלַמֵּד בְּנֵי יְהוּדָה קָשֶׁת הִנֵּה כְתוּבָה עַל סֵפֶר הַיָּשָׁר.
(א) הלא היא כתובה . דבר זה נכתב בתורה שאמר לו יעקב ליוסף ( בראשית מח יט ) : זרעו של אפרים יהיה מלא וגו' , אימתי , ביום שעמדה חמה ליהושע , נתמלא כל העולם שמעו של יהושע , ויעמד השמש בחצי השמים ולא אץ לבא כיום תמים :
ספר הַיָּשָׁר
.שם של ספר שירה עתיק שאבד, ונכתבו בו עלילות גבורה ושירי גבורה של בני ישראל
הספר נזכר רק פעמיים בתנ"ך :יהושע י' 13-12: "אָז יְדַבֵּר יְהוֹשֻׁעַ לַה'..., וַיֹּאמֶר לְעֵינֵי יִשְׂרָאֵל: שֶׁמֶשׁ בְּגִבְעוֹן דּוֹם וְיָרֵחַ
בְּעֵמֶק אַיָּלוֹן. וַיִּדֹּם הַשֶּׁמֶשׁ וְיָרֵחַ עָמָד עַד יִקֹּם גּוֹי אֹיְבָיו, הֲלֹא הִיא כְתוּבָה עַל סֵפֶר הַיָּשָׁר. וַיַּעֲמֹד הַשֶּׁמֶשׁ בַּחֲצִי הַשָּׁמַיִם וְלֹא אָץ לָבוֹא כְּיוֹם תָּמִים"
שמואל ב, א' 18-17: "וַיְקֹנֵן דָּוִד אֶת הַקִּינָה הַזֹּאת עַל שָׁאוּל וְעַל יְהוֹנָתָן בְּנוֹ. וַיֹּאמֶר: לְלַמֵּד בְּנֵי יְהוּדָה קָשֶׁת, הִנֵּה כְתוּבָה עַל סֵפֶר הַיָּשָׁר".
Wikipedia: Sefar haYashar (midrash)
The Sefer haYashar (first edition 1552) is a Hebrew midrash also known as the Toledot Adam and Dibre ha-Yamim be-'Aruk. The Hebrew title may be translated Sefer haYashar - "Book of the Upright Man" - but it is known in English translation mostly as The Book of Jasher following English tradition. The book is named after the Book of Jasher mentioned in Joshua and 2 Samuel.[1]Although it is presented as the original "Book of Jasher" in the translations such as that of Moses Samuel (1840), it is not accepted as such in rabbinical Judaism, nor does the original Hebrew text make such a claim...The earliest extant version of this Hebrew midrash was printed in Venice in 1625, and the introduction refers to an earlier 1552 "edition" in Naples, of which neither trace nor other mention has been found. The printer Joseph ben Samuel claimed the work was copied by a scribe named Jacob the son of Atyah, from an ancient manuscript whose letters could hardly be made out...The Venice 1625 text was heavily criticised as a forgery by Leon Modena, as part of his criticisms of the Zohar as a forgery, and of Kabbalah in general. Modena was a member of the Venetian rabbinate that supervised the Hebrew press in Venice, and Modena prevented the printers from identifying Sefer ha-Yashar with the Biblical lost book...Despite Modena's intervention, the preface to the 1625 version still claims that its original source book came from the ruins of Jerusalem in AD 70, where a Roman officer named Sidrus allegedly discovered a Hebrew scholar hiding in a hidden library. The officer Sidrus reportedly took the scholar and all the books safely back to his estates in Seville, Spain (in Roman known as Hispalis, the provincial capital of Hispania Baetica). The 1625 edition then claims that at some uncertain point in the history of Islamic Spain, the manuscript was transferred or sold to the Jewish college in Cordova. The 1625 edition further claims that scholars preserved the book until its printings in Naples in 1552 and in Venice in 1625. Apart from the preface to the 1625 work, there is no evidence to support any of this story.