This is one scroll from the complete Buddhist canon (Skt. Tripiṭaka; J. issai kyō) that Empress Kōmyō (701–760) commissioned for her deceased parents, the (Skt. Ajātaśatru-kaukṛtya-vinodana-sūtra; Ch. Asheshiwang jing; J. Ajaseō kyō). The date on the scroll from 740 (Tenpyō 12) with a votive text by Empress Kōmyō is why the canon is known as the Gogatsu tsuitachi kyō (“First Day of the Fifth Month Sutras”). It is estimated that 6,500 to 7,000 scrolls were copied over the course of about twenty years.
 
SAIKI RyokoEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.347, no.51. 

This is one of the scrolls from the Issai-kyō (collection of all the Buddhist scriptures) copied by the order of Empress Kōmyō in commemoration of her dead father. This Issai-kyō sutra collection is often called "First-of-May sutra" according to a prayer written at the end of the scroll by the Empress Kōmyō bearing the date May 1st, 740.
It took twenty years since 736 to copy all the lines of this sutra collection at the studio for sutra copying, and it is assumed that this sutra collection originally consisted of about seven thousand scrolls. This number implies that almost all the scrolls of Buddhist texts which existed in Japan in those days were included in this collection. Considering of the solemn calligraphic style and strict proofreading, this is the most excellent and representative copied sutra in Japan both in quality and quantity. The Ajase-ō-kyō (Ajātaśatru sutra) introduced in this article is based on the biography of Ajase, who became King by killing his father (the former king) and imprisoning his mother. Later on, Ajase became a Buddhist under the influence of Shaka (Śākyamuni or Buddha) and repented of his sin and was finally saved by Buddha. According to an old document kept in the Shōsō-in treasure house, it is known that this volume was copied in April, 742 by Kurehara-no-Ikuhito, who was working at the studio for sutra copying. 
Masterpieces of Nara National Museum. Nara National Museum, 1993, pp.72-73, no.54.