The following is an excerpt from Dr. Thomas Holland's Crowned With Glory, ©2000, used with permission.
Acts 8:37 - "I believe that Jesus Christ is the Son of God"
(See also this video.)
"And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God."
Here the testimony of this faithful and beloved African, the Ethiopian eunuch, does not appear in the Critical Text. Some have argued that the verse is not genuine because it is found in only a few late manuscripts and was inserted into the Greek text by Erasmus from the Latin Vulgate. It is true that the passage appears in the Latin Vulgate of Jerome. However, the passage also appears in a vast number of other Old Latin manuscripts (such as l, m, e, r, ar, ph, and gig). It also is found in the Greek Codex E (eighth century) and several Greek manuscripts (36, 88, 97, 103, 104, 242, 257, 307, 322, 323, 385, 429, 453, 464, 467, 610, 629, 630, 913, 945, 1522, 1678, 1739, 1765, 1877, 1891, and others). While there are differences even among these texts as to precise wording, the essence of the testimony still remains where it has been removed from other manuscripts.  Additionally, Irenaeus (202 AD), Cyprian (258 AD), Ambrosiaster (forth century), Pacian (392 AD), Ambrose (397 AD), Augustine (430 AD), and Theophylact (1077 AD) all cite Acts 8:37. (*Note: dates above are deaths of the authors, not dates of the quotes.)
If the text were genuine, why would any scribe wish to delete it?  In his commentary on the book of Acts, Dr. J. A. Alexander provides a possible answer. By the end of the third century it had become common practice to delay the baptism of Christian converts to assure that they had truly understood their commitment to Christ and were not holding to one of the various heretical beliefs prevalent at that time.  It is possible that a scribe, believing that baptism should not immediately follow conversion, omitted this passage from the text, which would explain its absence in many of the Greek manuscripts that followed. Certainly this conjecture is as possible as the various explanations offered by those who reject the reading.
Nevertheless, because of biblical preservation, the reading remains in some Greek manuscripts as well as in the Old Latin manuscripts. Clearly the reading is far more ancient than the sixth century, as some scholars have suggested. Irenaeus noted that "the believing eunuch himself: . . . immediately requesting to be baptized, he said, 'I believe Jesus Christ to be the Son of God'."  Likewise, Cyprian quotes the first half of the verse in writing, "In the Acts of the Apostles: 'Lo, here is water; what is there which hinders me from being baptized? Then said Philip, If thou believest with all thine heart, thou mayest'."  These statements, clearly quotations of Acts 8:37, appear by the end of the second century and at the first half of the third. We see that the passage was in common use long before the existing Greek manuscripts were ever copied. This in itself testifies to its authenticity and to the assurance of biblical preservation.
 The variants within the manuscripts that maintain this passage are minor. For example, 88 omits o Philippos (Phillip) and adds o eunouchos (the eunuch) and auto (very). Thus the verse reads in 88, "And he said, If thou believest with all thine heart, thou mayest. And the eunuch answered and said, I believe that Jesus Christ is the very Son of God." Such variants are common among the vast host of Greek manuscripts. It should be noted, nevertheless, that such variants do not constitute the removal of the passage from the text. Nor, are such variants of like significance as those that would remove the passage from the text.
 Metzger, A Textual Commentary On The Greek New Testament, 315-316.
 J. A. Alexander, The Acts Of The Apostle (New York: Scribner, 1967), vol. 1, 349-350.
 Against Heresies: I 1:433.
 Treatise 12:3:43.