It is in the Greek of Luke 4:11. That is where Satan was quoting, so of course that added short phrase is not going to be in the Old Testament.
NT:3379
mepote (may'-pot-eh); or me pote (may pot'-eh); from NT:3361 and NT:4218; not ever; also if (or lest) ever (or perhaps):
KJV - if peradventure, lest (at any time, haply), not at all, whether or not.
(Biblesoft's New Exhaustive Strong's Numbers and Concordance with Expanded Greek-Hebrew Dictionary. Copyright © 1994, 2003, 2006, 2010 Biblesoft, Inc. and International Bible Translators, Inc.)
It is in the Old Testament as far as St. Luke is concerned, and as far as the early church was concerned, because the early church used the Septuagint almost exclusively from the first century until the fourth, when St. Jerome translated the Vulgate using Hebrew and Latin texts. In retrospect, like much of Jerome’s work, this is useful but also creates the basis for a problem (not unlike the work of St. Augustine), in that it led to the idea that the Septuagint was somehow flawed and divergent from the Hebrew.
What we now know, and what Origen also demonstrated in the Hexapla, which was a work mocked by St. Epiphanius in arguably the least well-considered chapter of his Panarion, that being his invective against Origen and Origenists (this actually led to his tragic death; he set out for Constantinople after being baited by critics of St. John Chrysostom that St. John was harboring Origenist monks and was advocating Origen; this turned out to not be the case and St. Epiphanius turned back, only to die en route to his own diocese of Salamis of exhaustion and fatigue, for he was very elderly at the time; as I have mentioned elsewhere St. Jerome was also an outspoken critic of Origen and caused a slight incident between the Roman church and the Jerusalem church; he was also a great enemy of the pro-Origen bishop of Cagliari in Sardinia, who is to this day venerated as a saint by the Sardinians, who had the name Lucifer, which would be unfortunate for him in retrospect because as the Middle Ages progressed, people misread this translation of “day star” in Isaiah and thought Lucifer, which was actually a common name in ancient Rome and the name of a second century martyr, St. Lucifer, was the proper name of the devil, when in fact this was a translation; note that I do not accuse St. Jerome of deliberately translating it that way as Lucifer deliberately translates to “ligjt bearer” so this is a valid translation and the Vetus Latina, the Bible St. Jerome was commissioned to replace, translated it, from the Septuagint rather than the Hebrew and Aramaic texts, the same way (
quomodo de caelo cecidit lucifer qui mane oriebatur confractus ad terram qui inmittebat ad cunctas nationes).
At any rate, while the Vulgate is extremely useful because it provides a snapshot of the Hebraic scriptures the Jews of the fourth century regarded as reliable, and there is remarkably little variation between that and the Masoretic Text, which disproves the claims by some that the Masoretic Text was deliberately corrupted by the Jews to suppress Christological context (if such corruption occurred, which I doubt, it happened long before the Masoretes), but the inverse assumption, that the Septuagint is corrupt, can be shown as dubious by the discovery of the Dead Sea Scrolls, which contain texts which agree with Septuagint and Ethiopic scriptures.
So with regards to your main argument, that the devil was misquoting the Old Testament, why then would the early church use a corrupt scripture that aligned with this diabolical plot? One which is not referenced explicitly by the text and which has been implicated by no one that I am aware of other than yourself? Were you taught this interpretation, and if so, by who? I am really curious on this point, because, while this does not negate your point, since that would be an appeal to authority fallacy to claim otherwise, the relative lack of anyone else stating that this is the case, so far as I am aware, does suggest that it is less common (but it would be fallacious to disregard it on that basis).
It would however require an explanation as to why the early church permitted the use of the Septuagint without addressing such a problem, and why this interpretation is generally undocumented, as far as I know. And if you are aware of a Patristic commentator who supports your interpretation, I will readily eat crow on this issue.
You evidently have the same lack of spiritual sight that today's higher critics have a problem with too. In case you just don't 'get it', the modern NT versions omit that "at any time" idea from the Greek. Instead, they, like yourself, just look at the Psalms and know it is not in the original Psalms verse, so they figure it was a mistake in Luke 4:11 when it is not, because Satan added it to his quote.
On the contrary, I think the revised translation by the New Testament is still in error unless they had a manuscript basis for making the change; I don’t believe higher criticism is acceptable in omitting text from translations of the Scriptures in ways which differ from Patristic and historic precedent. The only case where higher criticism is useful is in ensuring, as I am arguing in another thread, that, for example, St. Paul’s use of the word arsenokoitai to refer to homosexuals is translated in a way which makes clear his intent when using it, and thus the recent NRSVue translation of it as “men who engage in illicit sex” is totally inadequate and the justification provided by the translators is completely unsatisfactory, and the whole affair is suspect, in that it suggests an effort to make the New Testament more politically correct so as to appease the powerful pro-homosexual interests which dominate the liberal seminaries which now control the mainline Protestant churches and also liberal factions who are trying to seize control of the Roman Catholic Church (and have even tried, without success, to get a foothold in Eastern Orthodoxy; there was a priest in Boston for the Orthodox Church of America who wrote an article for an OCA publication which appeared to condone homosexuality, and every single OCA priest in the state of Texas, about 250 priests, mostly married, some probably monastics at some smaller churches, and a great many others, wrote letters of protest, and the article was taken offline and retracted by the publication).
