Acts 9:5-6 KJV
⁵And he [Saul] said, Who art thou, Lord? And the Lord said, I am Jesus whom thou persecutest: IT IS HARD FOR THEE TO KICK AGAINST THE PRICKS. ⁶AND HE TREMBLING AND ASTONISHED SAID, LORD, WHAT WILT THOU HAVE ME TO DO? AND THE LORD SAID UNTO HIM, Arise, and go into the city, and it shall be told thee what thou must do.
All in bold type is omitted in modern versions. See per example the following.
Acts 9:5-6 AMP
And Saul said, “Who are You, Lord?” And He answered, “I am Jesus whom you are persecuting, now get up and go into the city, and you will be told what you must do.”
Acts 9:5-6 NASB
⁵And he [Saul] said, “Who are You, Lord?” And He said, “I am Jesus whom you are persecuting, but get up and enter the city, and it will be told you what you must do.”
The Acts 9:5-6 RV1885
And he [Saul] said, Who art thou, Lord? And he said , I am Jesus whom thou persecutest: but rise, and enter into the city, and it shall be told thee what thou must do.
The reason why the passage in question is omitted from virtually all modern versions (including both Majority Text editions) – frequently without even a footnote – is quite persuasive.
As Bruce M. Metzger puts it, “As far as known, no Greek witness reads these words at this place. They have been taken from Acts 26:14 and Acts 22:10, and are found here in codices of the Vulgate…
The spurious passage came into the Textus Receptus when Erasmus translated it from the Latin Vulgate and inserted it in his first edition of the Greek New Testament (Basel, 1516).
The 18th century Bible scholar, Johann David Michaelis, wrote (1749), “[This] long passage … has been found in not a single Greek manuscript, not even in those which have been lately (ca. 1785) collated by Matthai. It is likewise wanting in the Complutensian edition; but it was inserted by Erasmus [translating it from the Latin Vulgate], and upon his authority it has been adopted by the other editors of the Greek Testament… This passage then, which later editors have copied from Erasmus, and which is contained in our common editions, is not only spurious, but was not even taken from a Greek manuscript.”
The passage does not appear in the Complutensian Polyglot (1516) and noted as doubtful in Wettstein’s 1763 London edition, and since then it scarcely appeared in the main text and sometimes not even as a footnote in editions of the Greek New Testament and modern translations.