Britannica entry
“The Thousand and One Nights, collection of largely Middle Eastern and Indian stories of uncertain date and authorship. Its tales of Aladdin, Ali Baba, and Sindbad the Sailorhave almost become part of Western folklore, though these were added to the collection only in the 18th century in European adaptations.
As in much medieval European literature, the stories—fairy tales, romances, legends, fables, parables, anecdotes, and exotic or realistic adventures—are set within a frame story. Its scene is Central Asia or “the islands or peninsulae of India and China,” where King Shahryar, after discovering that during his absences his wife has been regularly unfaithful, kills her and those with whom she has betrayed him. Then, loathing all womankind, he marries and kills a new wife each day until no more candidates can be found. His vizier, however, has two daughters, Shahrazad (Scheherazade) and Dunyazad; and the elder, Shahrazad, having devised a scheme to save herself and others, insists that her father give her in marriage to the king. Each evening she tells a story, leaving it incomplete and promising to finish it the following night. The stories are so entertaining, and the king so eager to hear the end, that he puts off her execution from day to day and finally abandons his cruel plan.
Though the names of its chief characters are Iranian, the frame story is probably Indian, and the largest proportion of names is Arabic. The tales’ variety and geographical range of origin—India, Iran, Iraq, Egypt, Turkey, and possibly Greece—make single authorship unlikely; this view is supported by internal evidence—the style, mainly unstudied and unaffected, contains colloquialisms and even grammatical errors such as no professional Arabic writer would allow.
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It is clear that the expressions “A Thousand Tales” and “A Thousand and One…” were intended merely to indicate a large number and were taken literally only later, when stories were added to make up the number.
By the 20th century, Western scholars had agreed that the Nights is a composite work consisting of popular stories originally transmitted orally and developed during several centuries, with material added somewhat haphazardly at different periods and places. Several layers in the work, including one originating in Baghdad and one larger and later, written in Egypt, were distinguished in 1887 by August Müller. By the mid-20th century, six successive forms had been identified: two 8th-century Arabic translations of the Persian Hazār afsāna,called Alf khurafah and Alf laylah; a 9th-century version based on Alf laylah but including other stories then current; the 10th-century work by al-Jahshiyārī; a 12th-century collection, including Egyptian tales; and the final version, extending to the 16th century and consisting of the earlier material with the addition of stories of the Islamic Counter-Crusades and tales brought to the Middle Eastby the Mongols. Most of the tales best known in the West—primarily those of Aladdin, Ali Baba, and Sindbad—were much later additions to the original corpus.”
https://www.britannica.com/topic/The-Thousand-and-One-Nights