In Acts 12:25, we have the conclusion of the story of Paul and Barnabus' brief visit to Jerusalem (the church at Antioch had sent them with a gift of money for the poor saints at Jerusalem - see Acts 11:27-30). This verse also provides a bridge to the start of Paul and Barnabus' great first missionary journey, which starts in Acts 13.
In our English Bibles, there are two versions of this verse. Actually, in the Greek manuscripts there are three (or four versions of this verse), but we'll stick with English for the moment:
1. Paul and Barnabus returned TO Jerusalem when they had fulfilled their ministry and they also took with them John Mark (NRSV, NET, Holman Standard Christian Bible), OR
2. Paul and Barnabus returned FROM Jerusalem when they had fulfilled their ministry and they also took with them John Mark (KJV, NIV, ESV, NASB, NKJV, et al).
Now, of course, only one of these two sentences makes sense, because
a. the next verse (13:1) finds Paul and Barnabus in Antioch again (not Jerusalem),
b. the fact that they 'returned' means that they went back to where they originally came from (i.e. Antioch)
c. they took with them John Mark, who has earlier in Acts 12:12 has just been introduced to us for the first time (the prayer meeting which Peter visited after being released from prison was held in John Mark's mother' house), suggesting strongly that Jerusalem is where John Mark comes from, and that Paul and Barnabus were going away from Jerusalem back to Antioch.
So, it would appear (from our English Bibles) that the question is a no-brainer. Or, to put it another way, the first option ('they returned to Jerusalem') is so puzzling that it calls into question the intelligence of the text-critical scholars and Bible translators who have opted for this reading. More than that, if they are content to have the Bible itself reduced to nonsense, what does this say for their view of Scripture? No one has ever yet explained how this first reading makes the slightest sense in context.
In fact, this first reading is so ridiculous that most modern Bible versions (NIV, ESV, NASB) abandon their underlying Greek text at this point (the Nestle-Aland, or UBS text), and choose the reading that makes sense. Some scholars have called what these Bible translators have done a 'tradition of timidity' but, hey, here it is a choice between timidity and stupidity.
Why is it, then, that the scholars who have edited the modern critical Greek NT text (and some of the Bible translations mentioned above) have adopted the reading of some manuscripts which manifestly makes no sense?
The reason is obvious. Just like some medieval Catholics went on pilgrimages to worship relics (a shard of wood from Christ's cross, a finger bone of John the Baptist, some straw from the manger), so too modern textual critics treat certain scraps of ancient papyrus and cowhide codices of the Bible with virtual veneration. Even if what the words say on these ancient manuscripts makes no sense, they assure us that they must be the original wording of the NT.
Then, if this was not enough, they also argue that textual critics should prefer the Harder Reading!
Now, bear in mind here that it is not simply that a minority of manuscripts contain the ridiculous reading - the reading that makes no sense is found in the so-called 'earliest and best' manuscripts, as well as the majority of manuscripts (the Byzantine text is split, but the majority of Byzantine manuscripts have the ridiculous reading).
There are, however, quite a good number of manuscripts which correctly read that Paul and Barnabus returned from Jerusalem when they had fulfilled their ministry. Here is not the place to go into a technical discussion of how the different Greek readings arose, but it is not hard to see which was the original version.
One final note: Bruce Metzger, one of the editors of the UBS text, in his Textual Commentary explaining why the editors chose the dumber reading here, suggests that it would have been more natural for the author of Acts to specify the place where someone returned to (not where they came from). This is quite a good argument, but it overlooks one interesting little fact: the author of Acts was Luke, and if he was in Antioch at the time it would be more natural to describe Paul and Barnabus' return from his own perspective (i.e. where they returned from), rather than from Paul and Barnabus' perspective (where they returned to). So here we find another incidental piece of evidence of Luke's personal involvement in the story of the book of Acts (alongside other notes like the 'we' sections later in the book, e.g. Acts 16:11). In addition, Metzger's note probably explains why some scribes inadvertantly wrote the word TO, thus producing the blunder in their manuscripts at this point.