Where was the story first told that the title of Vanity Fair come to Thackeray in a "eureka moment" in bed?

Question

In his preface to Summer Lightning, P. G. Wodehouse makes reference to the story that William Makepeace Thackeray had a "eureka moment" in bed wherein he, Thackeray, suddenly had the idea for the title of his novel:

It is related of Thackeray that, hitting upon Vanity Fair after retiring to rest one night, he leaped out of bed and ran seven times round the room, shouting at the top of his voice.

Is this story found in Thackeray's own writings? If not, what is the earliest written source of this story (assuming that Wodehouse did not make it up, even if he may have embellished the "seven times" detail for humorous effect)?

Answer 1

This is from the recollections of Thackeray’s friend Kate Perry:

He told me, some time afterward, that, after ransacking his brain for a name for his novel, it came upon him unawares, in the middle of the night, as if a voice had whispered, “Vanity Fair.” He said, “I jumped out of bed, and ran three times round my room, uttering as I went, ‘Vanity Fair, Vanity Fair, Vanity Fair.’”

_{Kate Perry (1887). ‘Extracts from Miss Kate Perry’s Recollections of Mr. Thackeray’. In A Collection of Letters of Thackeray, 1847–1855, p. 178. New York: Charles Scribner’s Sons.}

As you surmised, Wodehouse exaggerated the number of times that Thackeray ran around the room.