There two translations:

1) Letter 61& Draft L Notes (I) Architecture of Hysteria :
p196-200 in Marie Bonaparte, Anna Freud, and Ernst Kris, (Eds.), The origins of psycho-analysis: Letters to Wilhelm Fliess, drafts and notes, 1887-1902, Sigmund Freud, London: Imago, 1954
Eric Mosbacher & James Strachey, Translators.
Available at www.LacanianWorksExchange.net /Freud

2) p238 – 242 of ‘The Complete Letters of Sigmund Freud to Wilhelm Fliess 1887-1904’ : Translated and Edited by Jeffrey Maoussaieff Masson: The Belknap Press of Harvard University Press, Cambridge, Massachusetts, and London, England: 1985
Jeffrey Maoussaieff Masson, Translator
Available at www.LacanianWorksExchange.net /Freud

In Draft L Notes (I) Architecture of Hysteria is an early reference to identification – see citation below.

Citation

-Interpretation of Dreams. SE IV p150-151
P5 6th February 1957 Seminar IV, EC Collective’s translation.
See Seminar IV The Relation from Object (La relation d’objet) & Freudian Structures (1956-1957) : from 21st November 1956 : Jacques Lacan, on this site /4 Jacques Laca (19561121) or Session of Seminar IV Identification with the Phallus : 6th February 1957 : Jacques Lacan, at this site /4 Jacques Lacan (19570206)

P5, We are thus finally led to ask the question of what is implicit here, and perpetually called into question by this very critique that is, the notion of identification, which is latent, present, emerging at every moment and then disappearing again in Freud’s work, since its very origins. For the implications of these identifications are already in The Interpretation of Dreams[19], which reaches its major point of explication when Freud writes Group (Mass) Psychology and the Analysis of the Ego[20], in which there is a chapter explicitly devoted to identification. This chapter has the goal of showing us – as happens very frequently, as it is the merit of Freud’s work to show us – the greatest perplexity on the part of the author.

FOOTNOTE [19]

19 Probably Freud S. (1900) Interpretation of Dreams SE IV pp. 150-151. Chapter IV Distortion in Dreams Information see The Interpretation of Dreams (Die Traumdeutung) : 6th November 1899 (published as 1900) : Sigmund Freud, on this site /4 Sigmund Freud (18991106). See www.Freud2Lacan.com.

Identification is most frequently used in hysteria to express a common sexual element. A hysterical woman identifies herself in her symptoms most readily – though not exclusively – with people with whom she has had sexual relations or with people who have had sexual relations with the same people as herself. Linguistic usage takes this into account, for two lovers are spoken of as being ‘one’. In hysterical phantasies, just as in dreams, it is enough for purposes of identification that the subject should have thoughts of sexual relations without their having necessarily taken place in reality. Thus the patient whose dream I have been discussing was merely following the rules of hysterical processes of thought in expressing her jealousy of her friend (which incidentally she herself knew was unjustified) by taking her place in the dream and identifying herself with her by creating a symptom – the renounced wish. The process might be expressed verbally thus: my patient put herself in her friend’s place in the dream because her friend was taking my patient’s place with her husband and because she (my patient) wanted to take her friend’s place in her husband’s high opinion.¹

Footnote ¹, Sigmund Freud writes, I myself regret the insertion into my argument of excerpts from the psychopathology of hysteria. [SE IV p104] Their fragmentary presentation and detachment from their context cannot fail to detract from their enlightening effect. If, however, they serve to indicate the intimate connection between the topic of dreams and that of the psychoneuroses, they will have fulfilled the purpose for which they are inserted. [James Strachey’s footnote ; This is Freud’s first published discussion of identification, though he had referred to it earlier, in his correspondence with Fliess (e.g. in Letter 58 of 8th February 1897 and Manuscript L of 2nd May 1897 (see this text). Though he touched upon the subject here and there in later publications, his first lengthy consideration of it after the present one was more than twenty years later in Chapter VII of Group Psychology (Freud 1921c)*. The different topic of identification as part of the dream-work is discussed below on SE IV p320f]

* {see SE XVIII p69-143 : published bilingual by www.Freud2Lacan.com – Information Mass (mistranslated as Group) Psychology and the Analysis of the Ego : 1921 [1922] : Sigmund Freud on this site (19210101 or Index of Sigmund Freud’s texts}